6- Aromatic Compounds, Carbonyls, Nitrogen Compounds, Polymers, Analysis Flashcards
Formula of benzene
C6H6
What are the two ways of representing a benzene
kekulé model and delocalised model
What is the kekulé model
1865 germana chemist
Benzene made up of a planar ring of carbon atoms with alternating single and double bond between them
Each carbon atom is also bonded to one hydrogen atom
How was the kekulé model layer adapted to include
To say that the benzene molecule was constantly flipping between two forms ( isomers) by switching over double and single bonds
What proved kedulé structure can’t be completly correct
You would expect there to always be 3 bonds with the length c-c bond ( 154pm)
Theeee bonds with the length. C=C (134pm)
However x-ray diffraction studies have shown that all the carbon-carbon bonds on benzene have the same length ( 140pm) ( the bonds are equal length)
What is the delocalised model
Says that the p-orbitals of all 6 carbon atoms overlap to create pi system
The pi system is made up of two ring shaped clouds of electrons, one above and one below the plane of 6 carbon atoms
All bonds are the same length because all the bonds are the same
Do the electrons belong to a specific carbon atom in the delocalised model of benzene
No
They are delocalised
How is the delocalised model represented
As a circle inside the ring of carbons rather than as double or single bonds
What is the enthalpy changed called when a halogenation atom occurs
The enthalpy change of hydrogenation
The hydrogenation of benzene expremintalt is ……. Exothermic than expected, so …
Far less
So more energy must have been put into break bonds in Bernese than would be needed to break bonds in the kekulé structure
Is the benzene more or less stable that the kekulé structure would be
More
What else except less exothermic enthalpy change of hydrogenation shows that benzene is more stable than the kekulé model would suggest
Resistance to reaction
What is the stability of keklué through to be due to
Delocalised ring of electrons
What are compounds containing benezene rings called
Arenes or aromatic compounds
What is it called when the functional group for benzene is not the priority group
Phenyl
What should a benzene with an OH group attached be called
…..phenol
What conditions would be needed to have benzene undergo similar electrophilic addition reaction as alkenes
Hot benzene
UV
Why is benzene very stable
Delocalised ring of electrons above and below carbon atoms
They spread of the negative change
Why do benzenes not as strongly attract electrophilles as C=C double bond in alkenes
In alkenes the pi bond in the c=c bond is an area of localised high electron density, which strongly attracts electrophiles. In benzene, this attraction is reduced due to the negative charge being spread out.
Benzenes tend to react by electrophilic ……
Substitution
What is an electrophillic substitution reaction of benzene
Hydrogen atom being substituted by an electrophile
2 step mechanism, addition of electrophile to form a positively charged intermediate , followed by a loss of H+ form the carbon atom attached to the electrophile , this reforms the delocalised ring
What helps to make good electrophiles for benzene
Halogen carriers
What does an electrophile have to have to be able to attack a stable benzene ring
Strong positive charge
What do halogen carriers do
Accept a lone pair of electrons form a halogen atom on an elctophile,
As the lone pair of electrons are pulled away the polarisation in the molecule increases and sometimes a carbocations is formed. This makes the electrophiles stronger
Examples of halogen carriers
Aluminium halides
Iron halide
Iron
What do halogen carriers help
Halogens substitute into benzene ring
Explain a benzene will react with halogens
(Halogenation)
- in the presence of an aluminium chloride catalyst, AlCl3
- the catalyst polarieses the halogen, allowing one of the halogen atoms to act as an electrophile
- during the reaction, a halogen atom is subsitiutued in play of a H atoms- called halogenation
Friedel-crafts reactions are really usefull in forming …
C-C bonds in organic synthesis
How are friedel-crafts reactions carriers out
Refluxing benzene’s with a halogen carrier and either a haloalkanes or an acyl chloride
How many types of friedel-crafts reactions are there
2
What are the two types of friedel-craft reactions
Friedel-crafts alkylation
Friedel-crafts acylation
What is Friedel-crafts alkylation
Puts any alkyl group onto a benzene ring using a haloalkanes and a halogen carrier
Friedel-crafts alkylation general reaction
C6H6 + R-X ——-> C6H5R + HX
What is friedel-crafts acylation
Substituted an acyl group for an H atom on benzene
You have to reflux benzene with acyl chloride instead of a choloalkame
This produced phenylketones
What does friedel-crafts acylation produce
And what is the exception
Phenylkerines
( unless R=Hm in which case an aldehyde called benzenecrabaldehyde or benzaldehyde is formedj
What is rhe general equations for a friedel-crafts acylation
C6H6 + RCOCl —-(reflux and AlCl3) —> C6H5COR + HCl
What do you needed to do to benzene to get nitrobenzene
Warm benzene with conc nitric acid and conc sulfuric acid
When you warm benzene with conc nitric acid and conc sulfuric acid you get nitrobenzene
What does rhe sulfuric acid do
Acts as a catalyst, it helps make nitroniym ion
NO2+, which is an electrophile
- It’s regenerated at the end of the reaction mechanism
What 2 equations show sulphuric acid acting as a catalyst in benzene to nitrobenzene
HNO3 + H2SO4 —-> H2NO3+ + HSO4-
H2NO3+ —-> NO2+. + H2O
What is mononitration
One NO2 group added
If you only wanted me NO2 group added to benzene to form nitrobenzene
What do you need to do
Keep the temperatures below 55°c
What 3 problems with kekulé model
Lack of reactivity of benzene
Thermodynamic stability of benzene
Bond lengths
How does lack of reactivity show a problem in the kekulé model
Based on kekulé model, benzene should decolorise bromine water
This doesn’t happen so far less reactive then kekulé model would suggest
How does thermodynamic stability of benzene show a problem in the kekulé model
Enthalpy of hydrogenation to cylcohenzae is is -119 kjmol-1
So you would expect hydprgenationof benzene to be -357kjmol-1
Yet it is -208 moldm-3
So more stable than expected with the kekulé model
What is conjugation (benzene)
Describe how electrons are delocalised across the whole molecule
What is the valence bond theory (benzene)
Explains bonding in benzenes as a series of unhybridised p-orbitals which overlap forming a cloud of e- density above and below the molecule
Which spreads e- stabilising the molecule
What type of reaction is a nitration of benzene
Electrophilic substitution
What are the conditions for a nitration of benzene
Conc sulphuric acid
50°c
What would happen if you increased temperature of nitration of benzene above 70
Claus further substitution
Equation to generate a nitronium Electrophilie ( in-situ)
HNO3 + H2SO4 —> NO2+ +HSO4 + H2O
What are some examples of halogen carriers
FeBr3
AlBr3
What would be the regeneration of a FeBr3 halogen carrier
H+ + FeBr4- —> FeBr3 + HBr
What is another name of methylbenzene
Toluene
What is a benzene with a Carboxylic group attached called
Benzoic acid
What is a benzene with NO2 attached called
Nitrobenzene
What benzene is not the highest priority what is it called
Phenyl group
What is a benzene with a NH2 attached called
Phenylamine
What is the common name for phenylamine
Aniline
What is benzene with a OH group attached. Called
Phenol
Is the relative density of benzene lower or higher than that of an alkene
Lower
What are the conditions of nitration of benzene
Conc H2SO4
500ºc
(HNO3)
What will happen in nitration of benzene if you increases the temperature above 70
Further subistutuon
What type of reaction is nitration of benzene
Electrophilic subsitutuon
Formation of br+ Electrophile with a halogen carrier
Br2 + FeBr3 —> br+ +FeBr4-
Solubility of phenols
OH group forms h bonds with h20 so mildly soluble
But the benzene ring is non polar so not that soluble
Know how a phenol acts as an acid
(About releasing H+ )
Learn the diagram
When phenol reacts with a strong base, what kind of ion forms
Phenolate
What is the name of position 2/6 on benzene
Ortho
What is the name of position 3/5bon benzene
Meta
What is the name of position 3on benzene
Para
What position/s does an electron donation group activate
Ortho
Para
What are some examples of electron donation groups
OH
Alkyl groups
NH2 or NHR
F, Cl, Br, I
What position/s does electron withdrawing group activate
Meta
(By deactivating Ortho / para )
What are some example of electron withdrawing group s
NO2
COOH
COOR
SO3H
CHO
CN
NR3+
What kind of conditions will phenol react with bromine
Mild
Why is phenol more reactive to Electrophilies than benzene
Lone pairs on OH can contribute e- density into ring
Why are phenol more likely to undergo Electrophilic substitution than benzene
One of the lone pairs of electrons in a p-orbital of the oxygen atom overlaps with the delocalised ring of electrons in the benzene ring
So the lone pair of electrons form the oxygen atom is partially delocalised int the pi system
Increases the electron density of the ring
Making it more likely to be attacked by electrophiles
In an unsubstitutec benzene, all carbon atoms are the same so electrohpiles react with .,,,
Any
What do electron donating groups do the electron density
They have electrons in orbitals that overlap with the delocalised ring and increase its electron density
In particular they increase density at carbons 2, 4, 6
What does electron withdraw ring group do to electron density (how)
Doesn’t have any orbitals that can overlap with the delocalised ring
And it’s electronegative
So it withdraws electron density form the ring
It withdraws electron density at 2,4,6
Does phenol decolourise bromine water
Yes as it’s more reactive than benzene
What happens when penal is shaked with bromine water
OH is electron donating
So directs substituting carbons, 2 4 6
Insoluble in water and precipitates out
Smells of antiseptic
Phenol reacts with dilute nitric acid to give …
Two isomers of nitrophenol and water
Is it easier to nitrate phenol or benzene
And why
Phenol
Activating effect of OH group
How does phenol react with sodium hydroxide
At room temp in a neutralisation reaction
To form sodium phemoxide and water
Does phenol react with sodium carbonate
Why?
No
Phenol is not a strong enough acid
T or f
Aldehyde and ketones are carbonyl compounds
T
How are aldehydes and Carboxylic acids made
Oxidising primary alcohols
You can use acidified dichromate (vl) ions to mily oxidise alcohols
What is the orange to green colour change due to (oxidising alcohols )
Orange dichromate (vl) ion is reduced to the green chromium (lll) ion
You can ….. aldehydes and ketones back to alcohols
Reduce
What is used to show a reducing agent
[H]
What is the vernal equation for reducing an aldehyde to a primary alcohol
RCOH + 2[H] ——-> RCH2OH
What is the general equation to reduce a ketone to a secondary alcohol
H
l
RCOR +2[H] ———> R-C-OH
l
R’
What is the reducing agent normally for reducing aldehydes and ketones back to Alcon
S
NaBH4
(sodium tetrehyseiborate(lll)
Or
Sodium borohydride)
Normally dissolves in water with methanol
What happens in a nucleophilljc addition reaction.
A nucleophile attacks the molecule and an extra group is added to it
Describe how aldehyde and ketones are reduced back to alcohols
(The mechanism(
The reducing agent , supplied hydrogen ions
H- has a lone pair of electrons so it’s a nucleophile and can attack rhe delta+ carbon on the carbonyl group of an aldehyde or ketone
Then adds water
Hydrogen cyanide will react with carbonyls a what typeof reaction
Nucleophilic addition.
Hydrogen cyanide will react with carbonyls to produce
Hydroxynitriles
Is hydrogen cycandid a strong or weak acid or alkali
Weak acid
How does hydrogen cyanide dissociates in water
Partially to form H+ and CN- ions
Is CN- a nucleophile or an electrophile
Nucleophile
Hydrogen cyanide will react with carbonyls, describe the mechanism
The CN- ion attacks the slightly postivibe carbon atom and donates a pair of electrons to it. Both electrons from the double bond transfer to the oxygen
The H+ (from hydrogen cyanide or water ) bonds to the oxygen to form the hydroxyl group
Hydrogen cyanide will react with carbonyls to produce a hydroxynitrile.
What are the dangers and what should be done to mitigate this risk
Hydrogen cyanide is a highly toxic gas
When thus reaction is done in the laboratory a solution of acidified sodium cyanide is used instead to reduce the risk
The reaction should be done in a fume cupboard
What can be used to test for aldehydes and ketones
2,4-dinitrophenylhydrazine
What is 2,4-dinitrophenylhydrazine (2,4-DNP) also known as
Brady’s reagent
Describe the 2,4-dinitrophenylhydrazine test form aldehydes and ketones
When it’s dissolved in methanol and conc sulfuric acid it will react with carbonyl groups to form a bright orange precipitate
This only happened with c=o groups, (not COOH) so only tests for aldehydes and ketones
How is the orange precipitate form the 2,4-dinitrophenylhydrazine test for aldehydes and ketones, used to know exactly which carbonyl compound it produced.
It’s a derivative of the carbonyl compound. Each carbonyl compound produces a crystalline derivative with a differnt melting point
So measure the melting pound of the crystals and compare it against the known melting points of the derivatives, you can identify the carbonyl compounds
What test lets you distinguish between a aldehyde and a ketone, and what basic fact does it use
Tollens reagent
That an aldehyde can be easily oxidised to a Carboxylic acid but a ketone can’t
What is tollens reagent
Colourless solution of silver nitrate dissolved in aqueous ammonia
How is tollens reagent used to test for an aldehyde
When heated togetehr in a test tube ,the aldehyde is oxidised and the silver ions in the tollens reagent are reduced to silver causing a silver mirror to form
The test tube should be heated in a breaker of hot water, rather than directly over a flame
What can tollens reagent also be called
Ammoniacal silver nitrate
What equation shows tollens reagent reaction
Ag(NH3)2. ^+ (aq) +e- —> Ag(s). + 2NH3(aq)
In synthesis of organic solids the desired products will oftern by ……
Trapped in a solvent / reaction mixture
How do you carry out reduced pressure filtration
- Place filter paper into the Bucner funnel and wet with a few drops of the solvent used in the reduction
2.turn on the vacuum pump to apply suction to the filter paper - can check suction be putting hand over Büchner funnel
3.slowly pour the reaction mixture into the filter paper - Rinse the crystals with more solvent and leave under suction for a few minutes for drying
Describe purification by recrystallisation
- War, a fixed volume of solvent using a water bath
- Tip impure sample into a second conical flask
- Slowly add the hot solvent to the impure sample until it dissolves ( add minimum amount of solvent needed)
- Once the impure produce has dissolved, allow the suction to cool. Pure crystals should start toform in the conical flask
- When crystals stop forming, obtain the dry crystal by reduced pressure filtration
What is reagent used to test for carbonyls
2,4 - DNP
Or
(Brady’s reagent)
Or
DNPH
Explain the steps of the test for a carbonyl
1) add excess 2,4 - DNP to a clean test tube
2j add unknown solution
3) if no crystals form add a few drops of sulfuric acid
4) if carbonyl is present an orange precipitate will form
What reagent is used to distinguish between an aldehyde or a ketone
Tollens regent
What is tollens reagent
Silver nitrate in a solution of ammonia
What isnthe ionic Eq for rhe silver mirror test
And what type of reaction is it
Ag+ ( aq) + e- —> Ag(s)
Reduction
What is a positive test for the tollens reagent
Silver mirror forms
Describe the C=C bond based on what kind of reactions it undergoes
High electron density so easily attracts (susceptible) to electrophiles
Describe the C=O bond based on what kind of reactions it undergoes
Permientdipole (polar bond)
Slightly positive carbon will react with strong nucleophile
What type of reaction is a carbonyl to an alcohol
Nuclophilic additon
Or
Reduction
What is a reducing agent represented by
[H]
How many moles of reducing ages is used to reduce an aldehyde or ketone
2
What is used to reduce and aldehyde or ketones and into what
Sodium borohydride (naBH4) and H2O
Alcohol
What is was way of extending the carbon chain
Addison of cyanide to am aldehyde or ketone
Describe the test to distinguish between an aldehyde and a ketone
1) a few drops of silver nitrate into a test tube
2) add dilute ammonia - tollens reagent forms
3) add approx, same amount of unknown solution
4) leave test tube in a water bath at 50°c
5) if silver mirror forms an aldehyde is present
What is the name of COOR
A Carboxyl functional group
What is another name for 2-hydroxybenzoicacid
Salicyclic acid
What are Carboxylic acids used In
Medicines
Food
Citrus fruits
Drinks
Describe the solubility of a Carboxylic acid
The oh group can from hydrogen bonds with water ( and the c=o group )
When do Carboxylic acids stop being soluble
When the carbon chain exceeds 4
Are carboxylic acids considered strong or weak acids
Weak acids so they partially dissociate into its ions
What is the PKA of a carboxylic acids
5
Suffix for a Carboxylic acid
Oic acid
What do carboxylic acids partially dissociate into
And where does the equilibrium lie
Carboxylate ions and H+ ions
To the left because most of the molecule doesn’t dissociates
Do hydrogen bonds exist between carboxylic acids
Why?
Yes
They are polar since electrons are drawn towards the o atom. H bonds are able to from between the highly polarised H(slightly positive) and O(slightly negative) atoms on other moelcuels
What is the suffix for salts of Carboxylic acids
Oate
How do carboxylic acids react with more reactive metals
In a redox reaction to form a salt and hydrogen
What salt would form with ethanoic acid and magnesium,I
Magnesium Ethanoate
What do carboxylic acids react with carbonates to from
Salt
Co2
Water
Carboxylic acids are neutralised with other …… to got, ….. and ……
Bases
Salt
Water
What bases can neutralise carboxylic acids
Alkalis
Metal oxides
How are acyl chlorides formed
Form reacting carboxylic acids with socl2
What functions group do acyl chlorides have
COCl
What is the general formula for an acyl chloride
CnH2n-1OCl
What is the suffix for acyl chlorides
Oyl chloride
What is the name for SOCl2
Thionyl chloride
What is replaced and by what when carboxylic acids react with socl2
The OH group in the acid is replaces by -Cl.
What is formed when propanoic acid reacts with socl2
Propanoyl chloride
SO2
Hcl
What happens when an acyl chloride reacts with coldwater o
Vigorous reaction producing Carboxylic acid and Hcl
What happens when an acyl chloride reacts with alcohols and in what conditions
At room temp
Ester and hcl
Acyl chlorides and alcohols
And
Carboxylic acids and alcohols
Both produce esters, what is the differnce
Acyl choride are irreversible, they are much easier and faster
What happens when an acyl chloride reacts with ammonia and in what conditions
A violent reaction at room temp producing a primary amide and hcl
What happens when acyl chlorides react with amines and in what conditions
Tom temp
A violent reaction producing a secondary amide
Each time Cl ( in acyl chlordies) is Substituted by an oxygen or nitrogen group What gas is given of
And what type of reaction is this
Hydrogen chloride
Nucleophilic addition-elimination reaction
Why would u react a phenol with an acyl choride to make an ester over with a Carboxylic acids
It’s faster
Phenol + acyl chloride :
Ester
Describe the reaction of ethanoic choride and phenol
Slowly at room tmep
To produce the ester : phenyl ethanoate and hydrogen choride
How to distinguisha Carboxylic acid
It’s the only organic compound acidic enough to react with carbonates
(Phenols can’t react with carbonates)
What is a Carboxylic acid derivative
Something that can be made form a Carboxylic acid
What is an ester mademfrom
Reacting an alcohol with a Carboxylic acid or a Carboxylic acid derivative
How to name an ester
The first bit comes form the alcohol
The second but comes from the Carboxylic acid ( swap the oic acid for oate)
What conditions are needed to make an ester from a Carboxylic acid and an alcohol
Acid catalysts and heat
What acidic catalysts is usually used when making an ester
Conc sulfuric acid
What is the reaction called when a Carboxylic acid and an alcohol react
Esterification
Is esterification reversible? So what does this mean for collecting products
Yes
You need to separate out the product as it’s formed
How can you separate a small ester from its products as it’s formed
Warm the mixture and just distil off the ester, because it’s more volatile than the other compounds
How can you separate a large ester from its products as it’s formed
Larger esters are harder to form so it’s best to heat them under reflux and use fractional distillation to separate the ester from the other compounds
What type of reaction is esterification as well
Condensation
What else is produced in esterification as well as the ester
Water
What is an acid anhydride made from
2 carboxylic acids
Acid anhydrides can be reacted with alcohols to make….
Esters
How is an ester made form an acid anhydride
Warmed with the alcohol
(No catalyst needed)
what are the products of acid anhydrides and alcohols
Ester and a Carboxylic acid
How can you separate the ester and Carboxylic acid (after forming when reacting acid anhydrides with alcohol)
Fractional distillation
When an acid anhydride is formed what else if made
A water
Look at how acid anhydrides and alcohols react
When an alcohol reacts with acyl chlorides what is formed
An ester and hydrogen chloride gas (toxic)
Esters are hydrolysed to from…..
Alcohols
What are the 2 ways to hydrolyse esters
Using acid hydrolysis
Or base hydrolysis
What is a similarity between acid hydrolysis and base hydrolysis of esters
Both types you get an alcohol
Explain acid hydrolysis of an ester
Splits an ester into a Carboxylic acid and an alcohol
You have to reflux the ester with a dilute acid, such as hydrochloric or sulfuric
Is acid hydrolysis of an ester reverisble
Yes
Acid hydrolysis of an ester is revserble
What is needed to push the equilibrium over to the right
Lots of water
Explain base hydrolysis of an ester
Reflux rhe ester with a dilute alkali, such as sodium hydroxide
What is made from base hydrolysis of an ester
Carboxylate slat
Alcohol
Is base hydrolysis of an ester reverisble
No
What else can be reacted with carboxylic acids to make acyl chlorides except for, socl2
To make what products
Pcl5
Acyl chloride , pocl3, hcl
What is acyl choroide susceptible to and why
Highly electropositive centre due to electronegative o and Cl
Susceptible to attack from nucleophile
In reaction of acyl Chlorides and alcohols, why would you need dry conditions
H2O would be a competing nucleophile and Carboxylic acid would also be made and lower the yield, they would then need separating
What is another name of alkali hydrolysis
saponification
What does saponification make
Carboxylate salt and alcohol
Which conditions favours the hydrolysis of esters
Alkaline
Forms a salt wich is very favourable so thus reaction goes to completion whereas acid hydrolysis doesn’t go to completion
Once acyl choice and ammonia have complained to make the amide and hcl
What then reacts
So what is included in the overall equation
Hcl and excess ammonia
Hcl + nh3 -> nh4+cl-
So you put 2 moles of ammonia and the product is not hcl it is NH4Cl
Once the acyl has reacted with primary amines and hcl is formed
What happens next
Hcl reacts with the primary amide forming
RNH3Cl
If one or more of the hydrogens in ammonia (NH3) is replaced with an organic group, what do you get
Amine
If nitrogen is bonded to 2 alkyl groups what is it called
Secondary amine
What do you get if nitrogen is bonded to four alkyl groups
A positively charged quaternary ammonium ion
Why are amines bases
There’s a lone pair of electrons on the nitrogen of the amine that’s able to accept protons.
Amines are neutralised by acids to make ….
Ammonium salts
What salt does ethylamine make when reacted with hcl
Ethylammonium chloride
How can aliphatic amines be make
Heating a haloalkanes with excess ethanolic ammonia (ammonia dissolved in ethanol)
Amines can be made from haloalkanes
what is made exactly, why
Mixture of primary, secondary and tertiary amines, and quaternary ammonium salts
As more than one hydrogen is likely to be substituted
How can you separate a mixture of amines
Fractional distillation
What will happen if bromoethane with react with ammonia
Forms ethylamine
This then can also react with bromoethane to form, diethylamine
How are aromatic amines made
Reducing a nitro compound
How are nitrocompounds reduced
And what does this make
Heat mixture of nitro compound, tin metal and conc. hcl
Under reflux
A salt
To get an aromatic amine from reducing a nitro benzene
What else is added
Sodium hydroxide
Reduction of nitro compound to an amine
What else is released
Water
T or f
Amides are Carboxylic acid derivative s
T
What are amides functional group
CONH2
Why do amides behave differently from amines
The carbonyl group pulls electrons away from the rest of the CONH2 group
What types of amides do you get
Primary and secondary
What does if an amide is primary or secondary depend on
How on atoms the nitrogen is bonded to
What group does an amino acid have
A basic amino group ( NH2) and an acidic Carboxyl group (COOH)
What is an a- amino acid
Both groups are attached to the same carbon atom - the a-carbon
What is the general formula for an a-amino acid
RCH(NH2)COOH
How do amino acids react with alkali
Carboxylic acid group in amino acid can react with an alkali to form a conjugate base - RCH(NH2)COO-
This can combine with a potivive ion to from a salt
How can amino acids react with an acid
Amino group meanwhile can react with an acid to from a salt of the conjugate acid
NH2 group on amino acid + HCL what salt group is fomred
Cl- H3N+
What do amino acids react with alcohols to form
What are the conditions
ester
Strong acid catalysts ( sulfuric )
What is a chiral carbon
A carbon atom which has 4 differnt group attached to it
Chiral carbons can be arranged in 2 ways so that 2 differnt molecules are made
What are these called
Enantiomers or optical isomers
What is an enantiomer
Non superimposable mirror image
If a molecule can be superimposed on its mirror image it ….
it’s achiral and so it doesn’t have an optical isomer
What does it mean that optical isomers are optically active
They rotate plane- polarised light
What is the difference between normal light and plane polarised light
Normal light vibrates in all directions , but plane polarised light only vibrates in one direction
What are enatiomers sometimes identified as
D or L
One enantiomer rotates the plane-polarised light …….. and the other….
Clockwise and the other rotates the same amount in the anti-clockwise direction
Are chiral compounds common in nature
Example
Yes
But you usually only find one enantiomers
Eg, all naturally occurring AA are L, most sugars are D
How do you draw 2 optical isomers
Identify the chiral carbon ( with 4 differnt substituents attached)
Draw one enantiomer in a tetrahedral shape , then draw a mirror image beside it
Do molecules have more than one chiral centre
They can
If a carbon is attached the same ring twice is it chiral
It can be if the order of atoms in the rings it differnt depending on which way you go rounf
If a molecule has more than one chiral centre
How many optical isomers will it have
More than 2
If a molecule has 2 chiral centres how many optical isomers are their
4
How to name a primary amine
Suffix - amine
Stem - chain
How to name secondary amines
N-
The shorted chain first
Then the longest. Chain with suffix
How to name tertiary amine
N,N-
Then the same rules as amine
What do amines make good….
Nucleophile as they can donate a pair of electrons
The bigger the amine the …. It is as a nucleophile
Worse
What can you describe an amine as
Lewis base - donates lone pairs
Brønsted lowery base - accepts protons
….. substituted amines are more basic
More
Why are more substituted amines more basic
Inductive effect
The EDG will enrich electron density so better at accepting protons
What happens to basic properties if NH2 is attached to benzene
Ewg
Lone pair delocalised into the ring nitrogen is less e- rich - less able to accept protons
Explain the boiling point in amines
hydrogen bonding So relatively high
Requires more energy to overcome
Describe the solubility in amines
Lower mass amines can form H bonds with water - effect lessens with larger amines
Soluble in organic solvents ( non/ less polar solvents)
Which functional groups will have distinctive smells
Ester
Desicbe addiction reactions
Two molcules join together to from a single product . Involves breaking a double bond
Desicbe elimination / dehydration reactions
Involves removing a functions group which is released as part of a small molecule
Often a double bond is bored
Desicbe a substitution reaction
A function group on a molecule is swapped for a new one
Desicbe a condensatiom reaction
Two molecules get joined together with the loss of a small molecule
Eg, water or hcl
Hydrolysis reaction description
Water is used to split apart a molecule, creating two smaller ones. Opposite of condensation
Desicribe oxidation reaction
Loss of election
Usually in organic means gaining an oxygen or loosing a hydrogen
Reduction reaction description
Reduction is gain or elections
In organic chem it usually means gaining a hydrogen atom or loosing an oxygen atom
Why do chemcial need a synthetic rote to get form one compound to another
Vital for designing medicines
Good more making imitations of useful natural substances when the real things are hard to extract
If your asked how to make one compound from another what do you need to include
Any special procedures ( eg, reflux)
The conditions needed
Saftey precautions eg, fume cupboards
Why do you reflux
Organic reactions are slow and substances usually flammable and volatile ( low bp )
If you stick them in a beaker and heat the, with a bunsen burner they will evaporate or catch fire before they have time to react
How does reflux work
Heated in a flask fixed to a Liebig condencer - so when mixture boils , the Vapor’s are condemned and recycled back into the fAsk . This stops reagent being lost form the fAsk and have time to react
How can organic solids be purified
Recrystallisation
dissolve solid in solvent to make a saturated solutions, then cool. Crystals form becasue wehn it cools the solubility falls - when it reaches the point it can’t stay in the solution the crystals form
1j very hot solvent added to impure solid until it just dissolves
2 ) this gives a saturated solution of the impure product
3j cool down slowly
4) crystals of the rod ict form as it cools . Impurities stay in solution ( as they are m much smaller amounts so take longer to crystallise out)
5) crystals removed by reduced pressure filtration and washed with ice cold solvent. Dried
When does recrystallisation only work ( solvent)
If the solid is very soluble in the hot solvent but nearly insoluble when the solvent is cold
If the product isn’t soluble enough in the hot solvent you won’t be able to dissoble it at all
If the product is too soluble in the cold solvent most of it will stay in the solution after cooling. When u filter it you will loose most of your product giving a low yield
Explain reduced. Pressure filtration
If your product is solid you can separate it from any liquid impurities by filtering under reduced pressure
Reaction mixture poured into the Büchner funnel with a piece of filter paper. The Buchner gunner is on top of a sealed sidearm flask which is conncectef to a vacuum line . Causing it to be plunder reduced pressure
Causes suction in the funnel so liquid can quickly pass into the flask and leave behind dry crystals
If they’re impure the melting point is…… and the boiling point is …..
Lowered
Raised
What is different about boiling points and melting points if very impure
Occur across a wide range of temps
How can you accurately measure melting point s
Put a small amount of the solid in a capillary tube and place it in a beaker of oil with a very sensitive thermometer.
Slowly heat, with constant stirring, until the solid just melts and read the temp
What can you do with a measure melting pint
Compare it to known data book values to determine its purity
What are the 2 types of polymerisation
Additon
Condensation
What type do polymerisation do alkenes join up
Additon
When is condensation polymers formed
Two types of monomers each of which has at least 2 fg
The fg group on one monomer reacts with a group on the other type of monomer to form a link
In condensation each time a link Is formed what happens
A small molecule is most ( oftern water)
What do condensation polymers include
Polyesters
Polyamides
What is the link between monomers in polyesters
Ester link
What is the bond formed between monomers in polyamides
Amide ( CONH)
How can condensation polymerisation be reversed
Hydrolysis
In practice, what is wrong with hydrolysis with water and what is done instead
Too slow
So down with acid or base
In polyamides will hydrolyse more easily y with acids or bases
Acids
What do polyamides hydrolyse into
(After being reacted with what in the Eq)
n dicarnoxylic acid
n diamine
2nH2O
Have a look at hydrolysis reaction on page 190
Will polyesters hydrolyse more easily with an acid or a base
Base
What is formed form hydrolysis of a polyester
Metal salt for the Carboxylic acid (dicarboxylic acid salt)
Diol
Carboxyl group reacts with amino group reacts to form
Amide group
What is an amide group
CONH
What is lost each time an amide link is formed
Water
What is reacted to make a polymaide
Dicarboxylic acid
Diamine
What reacts to make polyesters
Reactions between dicarboxylic acids and diols
Compounds were one Carboxylic acid group changed to an acyl chloride
How will it react differnt in condensation polymerisation
It will still from a polyester or a polyamide
Instead of water, hcl is eliminated
How do you draw the monomer form a polymer chain ( additon
Find the repeate unit
For an addition polymer the backbone of the repeat unit will always be 2 carbons long
You need to remove empty bonds that join onto the next relay until and replace central carbon carbon bond with a double bond
How do you find the monomers form condensation polymers
1) find the amide link or ester link then break down the middle
2) as h or oh on to both ends to find the monomer
( add h to O or N, or OH to C)
If the monomer units are dicarboxylic acids or diamine
Where does H2O come form
OH form dicarboxylic acid
H from amine
If the monomer units are dicarboxylic acids and a diol
Where does H2O come from
H from diol
And OH form CA to form an ester
If a molecule contains both amino and an alcohol and react with dicarboxylic acids in a condensation polymerisation reaction
What happens
Polymers contain amide and ester links
If a molecule has a CA and either an alcohol and amine group
What can happen
It can polymerise with itself to form a condensation polymer with only one monomer
Why is ammonia a good nucleophile
Can donate of e
What would the products look like for chlorobutane + ammonia =
Butylammonium chloride
Structural formula for butyl ammonium chloride
Ch3CH2CH2CH2N+H3Cl-
What do you do with butyl ammonium chloride to get your butyl amine
Work up with naOH
Ch3CH2CH2CH2N+H3Cl- add NaOH
What does it produce
CH3CH2CH2CH2NH2
NaCl
H2O
What can happen after butyl amine is produced
It’s still a nucleophile so at risk of undergoing further subsitituion
What lowers the risk of further substitution if you only want to make a primary amine
Excess NH3
As NH3 is a better nucleophile than the primary amine you have produced
Understand Eq when fu5her substitution happens on the amine made
What are aromatic amines made from
Nitro benzene + 6[H]
What are the conditions for synthesising aromatic amines from nitrobenzene
- Sn , conc hcl under reflux
- Excess naOH
Nitrobenzene + 6[H] produced what
phenylamine + 2H20
What is made form nitrobenzene + Sn and conc hcl under reflux
Phenyl ammonium chloride salt
How does cyanide form a new carbon carbon bond
CN-
Ion containing a negatively charged carbon atom, so it’s a nucleophile.
It’ll react with carbon centres that have a slight positive charge to crest a new carbon carbon bond.
What is the compound that is initially produced when a cyanide ion attacks a slight potivive carbon centre
Nitrile
What form of cyanide can you react with the slight positive carbon centre
KCN
NaCN
HCN
if C=O reacts with CN
what does rhe C=O bond go to
C-OH
Describe how cyanide ions react with haloalkanes
Nucleophilic substitution
Reflux haloalkanes with NaCN or KCN in ethanol. A nitrile is formed
Finish the Equation
R-X + CN- —->
R-C=- N + x-
Why is adding CN on useful
Once you have extended the carbon chain
It’s easy to convert nitrile to a new function groupo as nitrile group is very reactive
What can nitriles be used to form
Primary Amines
How can you reduce nitriles to primary amines
1) use lithium aluminium hydride (LiALH4- a strong reducing agent ) , followed by some dilute acid
2)also you can reduce the nitrile ( or hydroxynitiel) with sodium metal and ethanol
Can you reduce hydroxynitirles with LiAlH4
Yes
RCH2CN + ……
To form a primary amine
Finish the Eq
4[H] —> RCH2CH2NH2
LiAlH4 and sodium metal/ ethanol
What are the positives and negatives
Too expensive for industrial use but great for the lab.
What is used instead of LiAlH4 and sodium in the industry
Nitriles are reduced using hydrogen gas with a metal catalyst such as platinum or nickel at a high temp and pressure - called catalytic hydrogenation
What is reducing using hydrogen gas and metal catalyst called
Catalytic hydrogenation
RCH2CN + 2H2
What is made
RCH2CH2NH2
What are nitriles be hydrolysed to form
CA
How can nitriles be hydrolysed into CA
Reflux in dilute HCl
Then the nitrile group will be hydrolysed to form CA
RCH2CN +
Complete the equation to form a CA
2H2O + HCl —> RCH2COOH + NH4Cl
How can you tell if a synthetic route it likely to include formation of nitrile or hydroxynitrile
If the product of a synthetic route contains more carbon in the chain than the starting compound
Aside from CN what is another way of extending the carbon chain
Friended crafts reactions
What do you use to test for double bonds
Bromine water
Orange to colourless
How do you test for haloalkanes
Silver nitrate aq ( + ethanol)
White, cream ,yellow p
How do you test for phenols
You are testing the weak acid nature of
1) NAOH, strong base so will react with any acid
Acid - solid will dissolve, a colourless solution of a sodium salt will form
2) carbonate. Much weaker base , only react with strong acids not weak acids ( like phenols )
Strong acid - effervecnesce
Phenols- nothing
How do you test for CA
React with carbonates to form a salt , CO2 and water
Fizz and turn liemwater cloudy
How do you test for primary and secondary alcohols
Acidified potassium dichromate
Primary - organs - green
Secondary - orange - green
Tertiary - nothing
What is chromatography used for
To separate stuff in a mixture
Once the mixture is separated out you can oftern identify the differnt components
What are the 2 types of chromatography you need to know about
TLC ( thin layer chromatography)
GC ( has chromatography)
What is tlc
A solvent such as ethanol moved over a glass of plastic plate
Which is covered in thin layer of solid ( silica gel or aluminium powder)
Method to set up TLC
1) draw a pencil line near the bottom of the plate and put a spot of the mixture to be separated on the line
2) dip the bottom of the plate ( not the spot) into a solvent
3) as the solvent spreads up the plate , the differnt substances in the mixture move with it , but differnt distances so they separate put
4) when the solvent nearly reached the top of the plate , take the plate out and mark the distance that the solvent has moved ( solvent front) in pencil
How can you identify each spot on a TLC plate
Rf value
Then look up in table of known values
How to calculate Rf
Distance travelled by spot
—————————————-
Distance travelled by solvent
How far an organic molecule travels up the plate in TLC depends on what
How strongly its attracted to the layer of solid on the surface of the plate
What is the attractions between substance and the surface of the plate is called?
Adsorption
A substance that is strongly adsorbed
How will it move in TLC
Move slower
So wont travel as far as one that’s only weakly adsorbed
So they have differnt Rf values
What effects how strongly adsorbed a particular substance is to the plate in TLC
-Chemical properties such as polarity
- solid coating on the plate
- the solvent used
- extral values such as temperature
Small changes can effect Rf values
So what should be done to check TLc results
Once you have identified what you think an unknown compound is, it’s best to check your right by running a pure sample of the known substance alongside your unknown compound on a TLC plate
Identical substances should travel the same distance up the plate ( have the same rf vales )
Describe gas chromatography
The sample to be analysed is injected into a stream of gas
Which carries iron through a coiled tube coated with a Viscous liquid ( such as an oil) or a solid
The components of the mixture constantly dissolve in the oil or onto the solid , evaporate back into the gas and then redissolve as they travel through the tube
Time taken for the substance to pass through the coiled tube and reach the detector is called retention time and can be used to identify the substance
What is retention time (GC)
Time taken for the susbtance to pass through the soiled tube and reach the detector
Page 206
Ensure You can level a GC and TLC
What does a gas chromatogram show
A series of peaks at the times when the detector senses something other than the Carrier gas leaving the tube
What can gas chromatograms show
The identity of substances within the sample and their relative proportions
What does each peak on a chromatogram correspond to
A substance with a particular retention time
What are retention times measure form for each peak on a gas chromatogram
Zero to the centre of each peak
What can u use retention times in GC for
Can be looked up in a reference table to indentify the substances present
What does the area under each peak in a gas chromatogram represent
It’s proportional to the relative amount of each substance in the organism mixture.
Does tallest peak = most abundant substance
On a gas chromatogram
No
Not always
It’s about area
The area under the peak of a GC chromatogram gives the relative amount of a substance
What would u need to find after
Conc
What do you use to work out the concentration of a particular substance after GC
An external calibration curve
How do you use an external calibration curve along with GC to find conc
1) create a series of standard solutions of differnt conc of analyte - thus us just the substance you’ve chosen to detect for your calibration
2) one by one, inject your standard solutions into a GC instrument and record the result
3) calculate area under the peak of each repsonse for each standard solution
4) plot these values on a graph of area vs concentration
5) join your pouts up to crest an external calibration curve
Why would you run a blank when making a calibration curve
And what is a blank
A blank is a solution containing all the solvents and reagents used when making the standard solutions, but no analyste.
By subtractin the response of the blank form each of the responses of your standard solutions , you can find a corrected peak value - one that takes into account the fact of reagents and solvents on the peak area s
What 3 factors effect retention time
Solubility
Boiling point
Temperature of the gas chromatography instrument
How does solubility effect retention time
This determines how long each component of the mixture spends dissolved in the oil or on the solid and how long they spend morning along the tube in the gas. A highly soluble substance will spend more time dissolved, so will take longer to travel through the tube to the detector than one with a lower solubility .
How does boiling point effect retention time
A substance with a high boiling point will spemd more time condensed as a liquid in the tube than as a gas. This means it will take longer to travel through the tube than one with a lower boiling point
How does temperature of the gas chromatography instumsnt effect retention time
A high temperature means the substance will spend more time evaporated in the gas and so will move along the tube quickly, it shortens the retention time for all the substances in the tube
What does ammino acid + hcl form
Ammonium salt + Cl-
(NH3+)
What does amino acid + base form
H2O
Carboxylate salt
(Coo-)
What is a zwitterion
The H from the COOH is internally transferred to the NH2
To form NH3+ and COO- ion
(It’s dipolar )
What is the overall change of a zwitterion
0
What is an Isoelectronic point
The PH at wich the zwitterion is formed
Is the Isoelectronic point the same for all amino acids
No
If the PH is less than the Isoelectronic point what happens
The amino acid will behave as a base and gain a proton
(From the zwitterion the coo- goes to COOH)
What happens if the PH is greater than the Isoelectronic point
The amino acid will acid as an acid and will deprotenate
(From the zwitterion The NH3+ goes to NH2)
Ensure you can identify an amide linkage
NC=O
Check you can name amides
What 3 ways can you prepare amides
From carboxylic acids
Acyl chlorides
Acid anhydrides
How to prepare amides from carboxylic acids
CA + ammonium carbonate
Goes to ammonium carboxylate salt , co2 and H2O
Then from product dehydration/heat to. Amide + H2O
What ammonium carboxylate salt is made from
CH3COOH + (NH4)2CO3
CH3COO-NH4+
In preparation of CA, what needs to be in excess
And why
The CA
as RCOONH4 dissociates into RCOOH + NH3
excess of RCOOH shifts equlibrium to the left so increases RCOONH4 so more amide made after dehydrated
Ensure you can prepare amides form acylchorides and acid anhydrides
( done in carbonyl topic)
If you add sodium hydroxide solution to an unknown organic compound, and it gives off ammonia on heating, what is present
An amide
What does NMR stand from
Nuclear magnetic resonance
What is NMR
An analytical technique that you can use to work out the structure of an organic molecule
What is the sample of a compound placed in during NMR
A strong magnetic field
What is the sample exposed to in nmr
Range or differnt frequencies of radio waves
What happens to the sample when exposed to differnt frequencies of radio waves
The nuclei of certain atoms within the molecule absorb energy from the radio waves
The patter of the adsorption of radio waves from NMR, gives you what information
the position of certain atoms within the molecule and how many atoms of that type the molecule contains
You can peice this information together to work out the structure of the Molecule
What are the 2 types of NMR
Carbon -13
high resolution proton
What info does carbon-13 NMR give you
The number of carbon atoms that are in a molecule and the environments that they are in
What info does high resolution proton NMR give you
The number of hydrogen atoms that are in a molecule and the environments that they are in
What does an atoms environment depend on
all the groups that it’s connected to going right along the molecule - not just the atoms it’s actually bonded to
What do 2 atoms need to be to be in exactly the same environment
Be joined to exactly the same thing
How is a nucleolus partially shielded from external magnetic fields
By its surroundings electrons
What effect the electron shielding of a nucleus
Any other atom or group of atoms that are around it
Eg. If a carbon atom is boned to an electronegative atom that amounts to other shielding around the nucleus will decrease
Nuclei in a molecule feel differnt magenteic fields depending on their ……..
Nuclei in differnt …… will abosorb ……….. at ……..
Environment
Environments
Differnt amounts of energy
Differnt frequencies
What are you looking at in NMR
The differnces in absorbtion of energy between environments
How many carbon environments does chloroethane have and why
2 it’s carbons are bonded to differnt atoms
How many carbon environments does 2-Chloro propane have
1 c in a CHCl group bonded to (CH3)2
2 C in CH3 bonded to CHCl(CH3)
How many carbon environments do 1-chorlobutane have and why
4
The tow carbons in CH2 groups are differnt distances form the electronegative Cl atom so their environment is different
What do3s each peak show and represent in a carbon-13 NMR spectrum
The peak shows the frequencies at which the energy was absorbed by the carbon nuclei
Each peak represents one carbon environment
The differnces in absorbtion in carbon13 NMR spectrum are measured relative to what
A standard substance - TMS ( tetramethylsilane)
Why does TMS produce a single absorbtion peak in both types of NMR
It’s carbon and hydrogen nuclei are in the same environment
Why is TMS chosen as the standard
The absorbtion peak is at a lower frequency than just about Anything else
What value is TMS given and how are other substances meausred relative to this
0
All the peaks in other substances are measured as chemical shifts relative to this
What is a chemical shift
The difference in radio frequency absorbed by the nuclei ( hydrogen or carbon ) in the molecule that is being analysed and that is absorbed by the same nuclei in TMS
What symbol is used for a chemical shift ( describe it ) and what are they measured in
The same symbol used to say partial charge like on a polar bond C=O for example
Parts per million or ppm
Why would a small amount of TMS often be added to a sample
To give a reference peak on the spectrum,
What is the chemical formula for TMS
Si(CH3)4
What the first thing you should so when interpreting a carbon 13 spectra
Count the number of carbon environments
How do you count the number of carbon environments on a carbon13 NMR spectra
Count the number of peaks
If there is a peak at 0 don’t count it it’s just the TMS reference peak
If you have 3 carbon environments does that mean there are 3 carbons in your compound
No
Not necessarily there may be many carbons in the same environment
After using the carbon13 NMR spectra to find number of carbon environments what should you do next
Look up the chemical shifts in a shift diagram
What does the diagram on you data sheet for carbon13 NMR show
The chemical shifts experienced by carbon nuclei in differnt environments
What does the step in carbon13 NMR spectra interpretation for looking up to chemcial shifts in a shift diagram involve
Match up peaks in the spectrum with the chemical shifts in the diagram to work out wich carbon environment they could represent .
A peak at 10 may repecent c-c and a peak at 25 may represent c-c in the same molecule, they are just in differnt environments
Why is matching peaks to the groups in carbon13 NMR not always simple
Some chemcial shifts overall
So a peak at 40 for example could be due to c-c, c-Cl, c -br
After looking up chemical shifts in a shift diagram when interpreting carbon13 NMR spectra what is the last step
Take into account carbon environments, mr and fg present and try possible structures
What are optical isomers
Non superimposable mirror image of one another
What is a carbon atom with 4 differnt groups attached called
Chiral or asymmetrical carbon
What can 2 enantiomers of each other be called
+ -
D L
R S
What is a 50/50 mixture of enantiomers called
Racemic or racemate
How does Racemic mixture effect plane of polarised light
It has no overall effect
What do 2 enantiomers have in common
Identical chemcial and physical properties
What differs between enantiomers
Differnt effects on plane of polarised light
They have differnt reactions
What is condensation polymerisation
Polymerisation where a small molecule is eliminated
Used of polyglycolic acid
Drug delivery
Tissue scaffolding
What 2 things would u use to make a polyester from two monomers
Diole
Dicarboxylic acid
n diole + n dicarboxylic acid
How many waters are relaxed
(2n-1) H2O
What does alkaline hydrolysis of polyesters result in
Diole
Dicarboxylatesalt
What does acid hydrolysis of a polyester give
Diole
Dicarboxylic acid
Why are addition polymers not biodegrade
C-c bond is not susceptible to acid or alkaline hydrolysis
What does each peak on proton nmr represent
One hydrogen environment
Once you have a proton NMR spectra what’s the first thing Yaounde should do
Look up chemical shifts on a data diagram to identify possible environments
In proton nmr, the relative area under each peak tells you…
The relative number of hydrogen atoms in each environment
How can areas on a proton nmr be shown
Numbers above the peaks or integration trace
What is an integration trace
Shown with a line to show a Hight increase that is proportional to the area under each peak
What happens in proton nmr and not c13 nmr
The peaks in the spectrum split according to how the hydrogen environments are arranged
What is the splitting influences by?
And what is thus effect called
Hydrogen atoms bonded to neighbouring carbons
Spin-spin coupling
T or f
Only hydrogen nuclei on adjacent carbon atoms affect each other
T
What are the split peaks in proton nmr called
Multiplets
What determines how many spits there will be , what is this rule called
Always split into one more than the number of hydrogens on the neighbouring carbon atoms
Called n +1 rule
What do you call a peak that’s split into 2
Doublet
What do you call a peak that split into 3 and what for 4
Triplet
Quartet
If a peak is split into 2, how many hydrogen are on the neighbouring carbon
1
If there are three hydrogens on the neighbouring carbon how many does rhe peak split into
4
NMR spectra are recorded with the molecule being analysed in solution, what do you need to consider when using a solvent
Ordinary solvents like water or ethanol , the hydrogen nuclei in the solvent would add peaks to the spectrum and confuse things.
What is done to overcome hydrogen in the solvent affecting the proton nmr spectra
The hydrogen nuclei are replaced with deuterium (D)
They down a dorm radio wave energy so don’t add peaks to the spectrum
What is deuterium
An isotope of hydrogen with one proton and one neutron
How can you identify OH and NH protons
Run 2 spectra of the molecule , one with a little deuterium oxide (D2O) added
If an OH or NH is present it.l swap with the deuterium and the peak will disappear
Are all nuclei active in nmr spectroscopy
No
What are active in nmr
Spin 1 half nuclei = odd atomic number
Only active if they have spin
Eg, C13 H1 N15
What happens when nuclei are placed in strong magnetic field
They align with the field or against it (higher energy h
Differnt energy needed to make it go agasit the field wich depends on its environment
After it flips to the higher energy it relaxes back wich is monitored and plotted as a spectr
A spectra graph is a graph of absorption against ….
Frequency ( measured as chemcial shifts)
If only 1% of carbon atoms are 13C, how can it be detected
Samples used contain millions of the organic molecules so it’s still detected
What is the shielding effect on 13C nmr
Electrons surrounding atoms have their own magnetic field wich opposes the external field lowering the effect
What is the deshieldinf effect
If the C is attached to a more electronegative the electrons are pulled further away
Why is TMS used as a reference
12 equivalent H atoms , so one single intense peak
It’s protons are highly sheidled so nmr peak is upfield of other peaks
Non toxic, chemically inert , so won’t react with th sample
Low booling point so can distilled of and sued again
What 3 things can you obtain form a C13 NMR
1) the number of differnt carbon environments
2) the carbon environments
3) the relative ratio
What solvents are usually used in proton NMR
Ccl4
CDcl3
What is used to calibrate the proton nmr spectrum
TMS
What is the formula for chemcial shift calculation
Field of TMS - field measured X10^-6
———————————————-
Field for TMS
What do you call it if there are multiple hydrogen connected to the adjacent carbon ( proton nmr splitting)
Multiplet
Chromatography
What is retention time
The time taken for a compound to travel through the column to the detector
What are the area on each peak in a gas chromatographam show
amount of each compound
