Module 6 key information Flashcards
What is a sigma bond?
head-on overlap of orbitals between bonding atoms
What is pi bond?
sideways overlap of adjacent p-orbitals above and below the bonding atoms
Differences between a sigma bond and a pi bond? ( 3 comparisons)
1) sigma bond is the head-on overlap of orbitals, pi bond is the sideways overlap of orbitals.
2) sigma bonds have their electron density between bonding atoms, pi bonds have their electron density above and below the plane.
3) sigma bonds have a high bond enthalpy whereas pi bonds have a lower bond enthalpy because the electrons are further away from the nucleus.
What is benzene
A colourless liquid found in crude oil. It is a planar molecule with lots of points of contact
What is kekule’s model of benzene?
- 6 membered ring
- alternating single and double bonds
- P-orbitals overlap in one direction
- Pi electrons are localised
- C6H6
- Draw diagram of kekule’s model
Why was Kekule’s model disproved?
1) LACK OF REACTIVITY. COMPARED TO ALKENES- alkenes undergo electrophillic addition and C=C is lost whereas benzene undergoes electrophilic substitution so does not decolourise bromine water
2) THEY HYDROGENATION ENTHALPIES ARE LESS EXOTHERMIC THAN EXPECTED- benzene is more stable
3) LENGTH OF THE CARBON CARBON BONDS ARE ALL THE SAME LENGTH- single carbon bonds and double carbon bonds are of different length.
What is the delocalised model of benzene?
- 6 membered ring
- C6H6
- P-orbitals are perpendicular to the ring structure
- Adjacent P-orbitals overlap sideways creating a system of pi bond spread across the ring
- P-orbitals overlap in both directions
- Ring of electron density above and below the plane
- draw model out
Compare the two models of benzene?
SIMILARITIES: . 6 membered ring - each carbon bonded to 1 H -Sideways overlap of P-orbitals - Electron density above and below the ring DIFFERENCES: -K= p-orbitals overlap in 1 directions -D= p-orbitals overlap in both directions
- K= Pi electrons are localised
- D= Pi electrons are delocalised
-DRAW DIAGRAM OF BOTH
Another word for aromatic compounds?
Arenes
What group on a benzene ring give the name ‘——-benzene’
Alkyl groups up to C6H13
Halogens
Nitro groups
What groups on a benzene ring give the name ‘phenyl——–’
Alkyl groups with more than 7 carbons Alkyl chain with a functional group Amine group (NH2)
Structure of benzoic acid
C6H5(COOH)
Structure of phenol
C6H5(OH)
Structure of benzaldehyde
C6H5(CHO)
Why does benzene undergo electrophilic substitution?
Benzene delocalised electron above and below the plane which makes it stable. It does not want to break the delocalisation. The nucleophile is spread across the ring so requires a catalyst.
What are the conditions of nitration of benzene?
Conc sulphuric acid + nitric acid, 50 degrees (higher than 50 degrees will cause further substitution)
How is the electrophile formed? ( First part of the reaction) N
HNO3 + H2SO4 ———NO2+ + HSO4- + H20
……….
What are the conditions of halogenation of benzene?
Halogen carrier catalyst ( ALBR3 OR FEBR3)
How is the electrophile formed? ( First part of the reaction) H
CL2 + FECL3———————–FECL4- + CL+
What is another name for alkylation and acylation of benzene?
Friedel-crafts
What are the conditions of alkylation and acylation?
Halogen carrier catalyst
How do alkenes react with bromine thats different from benzene?
Alkene: No catalyst, addition reaction, loss of the double bond
Why does benzene require a catalyst?
Electron density more spread out across the ring, less electron density in one place. Need a stronger electrophile
How to name phenols?
The carbon bonded to the OH is always carbon 1
Why are phenols more reactive than benzene?
The Oxygen bonded to the benzene ring has 2 lone pairs. One lone pair can delocalise into the benzene ring. This increases the electron density in the ring making it a better nucleophile. Can attract electrophiles easier.
What test is used to test for phenols?
Add bromine water and it will decolourise and a white precipitate will form ( 2,4,6 tribromophenol)
Conditions for the Bromination of phenol?
Room temp and no halogen carrier catalyst.
Conditions for the nitration of phenol?
dilute nitric acid at room temp
forms 2-nitrophenol or 4-nitrophenol
Why can’t phenols react with COOH in an esterification reaction?
The lone pair of oxygen on phenol is not always available to attack which makes the OH a weaker nucleophole.
Why can phenols react with acyl chlorides to form an ester?
Acyl chlorides are more reactive due to 2 electronegative atoms surrounding the carbonyl compound
Can carboxylic acids react with NaOH OR Na2CO3?
Reacts with both as the negative charge can be spread over 2 electronegative O atoms. LOW PKA
Can phenols react with NaOH OR Na2CO3?
Reacts with NaOH but not NaCO3. NaCO3 is a weaker base. The negative charge cane move into the ring but the carbon does not stabilise it too well. MEDIUM PKA
phenol + NaOH= sodium salt + water
Can alcohols with NaOH OR Na2CO3?
Does NOT react with both. The negative charge has nowhere to go. HIGH PKA
What are the activators? Where do they direct substituents?
Alkyl groups 2,4,6 OH 2,4,6 OR 2,4,6 NH2 2,4,6 NHR 2,4,6
What are the deactivators? Where do they direct substituents?
Halogens 2,4,6 aldehydes 3 carboxylic acids 3 esters 3 amides 3 acyl groups 3 No2 3 CN 3 SO3H 3
Does the carbonyl in a carbonyl group act as an electrophile or a nucleophile?
electrophile because the oxygen is more electronegative. This means it is attacked by nucleophiles by nucleophilic addition.
Can primary alcohol be oxidised?
yes, by distilling to aldehyde and by reflux to a carboxylic acid
Can secondary alcohol be oxidised?
Yes, by reflux to a ketone
Can tertiary alchols be oxidised?
No, there is no H attached to the Carbon
Can carboxylic acids be reduced?
No
Can aldehydes be reduced?
yes, to primary alcohols
Can ketones be reduced?
Yes, to secondary alcohols
What is the oxidising reagent?
K2CR2O7/H2SO4 [O]
produces H2O too
What is the reducing reagent?
warming with NaBH4 (aq)
HCN is extremely poisonous so what do we use instead?
NaCN + H2SO4
Aldehyde + HCN= ?????
hydroxynitrile by nucleophilic addition
How to test for a carbonyl group?
Add a solution of 2,4 DNP ( solid 2,4 DNP dissolved in methanol and sulphuric acid)============ Pale orange solution
POSITIVE RESULT= ORANGE/YELLOW PRECIPITATE
How to determine between aldehyde and ketone?
Add tollens reagent ( silver nitrate in aqueous ammonia) at 50 degrees.
ALDEHYDE= silver mirror as aldehyde is oxidised to a carboxylic acid and silver is reduced
KETONES: nothing
Can carboxylic acids form Hydrogen bonds?
YES
Are carboxylic acids soluble?
Yes, up to 4 carbons. More than 4 carbons will be insoluble because as the chain increases the non-polar chain has a greater effect on solubility.
CARBOXYLIC ACID + BASES= ???
metal hydroxide = salt + h20
metal oxide= salt + h20
metal carbonate+ salt + co2 + h20 ( fizzing)
metal= salt+ hydrogen ( metal dissapears and fizzing)
What are the derivatives of carboxylic acids?
esters, acyl chlorides, acid anhydrides and amides
How do derivatives of carboxylic acids react?
nucleophilic substitution
How to name esters?
the part from the alcohol comes first and the second part end with oate
alcohol + carboxylic acid ( h2so4 as acid catalyst) =
ester + water
What is hydrolysis?
the chemical breakdown of a substance in the presence of water or in aqueous solutions
How is acid hydrolysis of esters done?
heated under refluc with dilute aq acid (catalyst)
Is acid hydrolysis of esters reversible or irreversible?
reversible so to make sure the reaction is complete add excess dilute acid
What is another word for the alkaline hydrolysis of esters?
Saponification
How is alkaline hydrolysis of esters done?
heat under reflux with dilute alkali
What are the advantages of alkaline hydrolysis of esters?
irreversible and carboxylate salt and alcohol is easier to separate ( distillation)
What does acid hydrolysis of esters produce?
carboxylic acid + alcohol
What does the saponification of esters produce?
carboxylate salt + alcohol.
React the carboxylate salt + HCL to form COOH
What do acyl chlorides end in?
oyl chloride
How do you prepare an acyl chloride?
Carboxylic acid + SOCL2 (thionyl chloride) ina fume hood
acyl chloride + HCL g and SO2 g
Why are acyl chlorides useful?
Used to make carboxylic acids, ester, primary and secondary alcohols because they are very reactive.( bonded to 2 electronegative atoms)
Acyl chloride + water=
carboxylic acid + HCL g
Acyl chloride + alcohol=
ester + HCL
Acyl chloride + phenol ( no catalyst) =
ester on phenol + HCL
Acyl chloride + phenol ( halogen carrier catalyst) =
friedal crafts acylation and will act as an electrophile
Acyl chlorife + ammonia=
Amide + HCL
HCL +Nh3= NH4CL
Acyl chloride + primary amines=
secondary amide +the primary amine cl-
How to from and acid anhydride?
carboxylic acid + carboxylic acid
forms also H20
How do acid anhydrides react?
React as an electrophile
+ phenol= ester on phenol = carboxylic acid
What determines if an amine is a primary, secondary or tertiary amine?
The number of carbons bonded to the N
If the NH2 is at the end of the chain, the name ends in? (naming primary amines)
‘AMINE’
eg: ethyl amine
If NH2 is not on the end of the chain, the NH2 becomes a ? (naming primary amines)
Substituent
eg: 3 amino propane
How to name secondary/tertiary amines?
If the same groups are attached to the N eg: di methyl amine If different groups attached to the N alphabetical order eg: ethyl di methyl amine
How to make aliphatic amines?
Haloalkane + conc ammonia solution = ammonium salt ( Nh3+Cl-)
ammonium salt + NaOH(aq) = amine + water + NaCl
How to secondary or tertiary amines?
Making primary alcohol can eventually lead to further substitution as the nitrogen still contains a lone pair
Primary amine + Haloalkane= secondary amine Cl-
Secondary amine + haloalkane = Tertiary amine Cl-
How to prevent further substitutions of a primary amine?
Excess ammonia as it is a better nucleophile than amine
Ethanol is used as a solvent as it is a weaker nucleophile than water so less likely to interfere and produce an alcohol
How to increase the chance of further substitutions of primary amine?
Add excess haloalkane as it promotes further substitution of the amine group
What is another way to form primary amines by reduction?
Nitrile + H2 ======== primary amine
Ni catalyst
How to make aromatic amines?
Nitration of benzene
nitrobenzene + 6[H] ============ phenylamine + 2h20
Sn/HCl conc
excess NaOH
UNDER REFLUX
How do amines act as bases?
Nitrogen has a lone pair and can form a dative bond with Hydrogen
NH3+CL-
(NH3+)2SO4 2-
What is the structural formula of an amino acid?
RCH(NH2)COOH
How do amino acids act as bases ?
The Nitrogen has a lone pair than can accept a hydrogen
How do amino acids act as acids?
The COOH loses Hydrogen and form a sodium salt + h20
How amino acid reacts with alcohols?
heat with sulphuric acid
ester and the NH2 becomes Nh3+
How to form primary amides?
acyl chloride + ammonia === primary amide + NH4CL
How to form a secondary amide?
Primary amine + acyl chloride ======secondary amide + amine chainNh3+Cl-
-amino acid + amino acid= secondary amide
(COOH reacts with the Nh2)
What is a structural isomer?
Compounds with the same molecular formula but the different structural formula
What is a stereoisomer?
Compounds with the same structural formula but a different arrangement of atoms in space
What is an optical isomer? (a version of a stereoisomer)
2 non-superimposable mirror images structures
What is another name for an optical isomer?
enantiomers
Do enantiomers have the same biological properties?
No,
maybe different tastes
What must compounds have to have optical isomers?
chiral carbon
a carbon bonded to four different atoms or groups of atoms
What must a compound have to have addition polymerisation?
Backbone consisting of carbon-carbon bonds
so each repeat unit has two carbons
What does condensation polymerisation mean?
Joining monomers together to form a polymer that results in the loss of a small molecule usually water.
What are the two ways to form a polyester?
One monomer has a COOH on one side and an OH on the other binds to another monomer with the same structure
OR
One monomer with COOH on both sides binds to another monomer with OH on both sides
BOTH FORM WATER
What are the two ways to form a polyamide?
One monomer has a COOH on one side and an NH2 on the other binds to another monomer with the same structure
OR
One monomer with NH2 on both sides binds to another monomer with COOH on both sides
What does hydrolysis mean?
The chemical breakdown of a compound using water
What does the acid hydrolysis of a polyester form?
carboxylix acid + alcohol
reagents (hcl(aq))
warm
What does the alkaline hydrolysis of polyesters form?
carboxylate salt (O-Na+) + alcohol
reagents( NaOH(aq))
warm
What does the acid hydrolysis of a polyamide form?
carboxylic acid + the NH2 becomes NH3+
What does the alkaline hydrolysis of polyamide form?
carboxylate salt + Nh2——–Nh2
How to form a nitrile?
Haloalkane + NaCN= nitrile + NaCL
nucleophillic substitition
solvent is ethanol
KNOW THE MECHANISM
How to form a hydroxynitrile?
aldehyde/ketone + HCN= hydroxynitrile
nucleophillic addition
How are nitriles reduced?
CH3CH2CH2CN + 2H2 === CH3CH2CH2CH2NH2
How are nitriles hydrolysed?
CH3CH2CN +2H20 +HCL(aq) =======CH3CH2COOH + NH4CL
heat
Apart from a nitrile, how else can you increase the carbon chain?
FRIEDEL CRAFTS:
alkylation
acylation
How to prepare an organic solid?
1) REFLUX= prevent reaction mixture from boiling dry, organic molecules have a low BP *know the diagram
2) FILTER UNDER REDUCED PRESSURE= *know the diagram
What is the purification method of an organic solvent?
- cool reaction mixture
- filter under reduced pressure
- recrystallize by dissolving impure solid in a minimum volume of hot solvent/water
- cool solution and filter solid under reduced pressure
- wash solid with cold solvent ad leave to dry
How to check if a substance is impure or pure?
obtain the melting point and compare to know values
pure= sharp melting point that is close to databook values
What does the mass spec determine?
the molecular mass from the molecular ion peak
What does the infrared spec determine?
functional groups
How do the bonds produce a spec with infrared?
Bonds absorb infared and vibrate
Causes covalent bonds to vibrate and absorb energy
What is the fingerprint region?
the region below 1500cm-1 that can be used to identify a particular compound using a compound using computer software or by physically comparing the data
What can IR be used in?
brethalysers
In paper Chromatography, what is the stationary phase and the mobile phase?
Stationary phase= chromatography paper
Mobile phase= solvent
How to work out the RF value?
Spot/solvent
If a spot does not move of the chromatography paper, what is it?
insoluble
Why must the chromatography line be drawn with a pencil?
So it does not smudge or interefere with the spots
What is the difference between TLC and paper chromatography?
Instead of chromatography paper, it is carried out on a TLC plate
What is the stationary phase in TLC?
a thin layer of adsorbent (silica gel)
What is the mobile phase in TLC?
Solvent
What does adsorption mean?
The substance is held on to the surface of another substance
What is the separation based on in paper chromatography?
solubility
What is the separation based on in TLC?
solubility and affinity
the higher the spot moves the more soluble and low affinity it has to the adsorbent
In TLC, what is used to put a small sample on TLC plate?
capillary tube
What are the ways you can view TLC?
non-destructive= TLC plate is impregnated with fluorescent material that glows under UV light destructive= Iodine reacts with compounds to form yellow-brown spots
How to carry out TLC?
A pencil line is drawn near the bottom of the plate and a small drop of a solution of the dye mixture is placed on it using a capillary tube. If any of this was done in ink, dyes from the ink would also move as the chromatogram developed.
When the spot of mixture is dry, the plate is stood in a shallow layer of solvent in a covered beaker using a watch glass. It is important that the solvent level is below the line with the spot on it.
The reason for covering the beaker is to make sure that the atmosphere in the beaker is saturated with solvent vapour. To help this, the beaker is often lined with some filter paper soaked in solvent. Saturating the atmosphere in the beaker with vapour stops the solvent from evaporating as it rises up the plate.
As the solvent slowly travels up the plate, the different components of the dye mixture travel at different rates and the mixture is separated into different coloured spots.
How to investigate a reaction using TLC?
Compare solvents at regular intervals. Use a control
In Gas chromatography what is the stationary phase and the mobile phase?
Stationary phase= carrier gas (inert)
Mobile phase = liquid adsorbent on solid support
How to carry out gas chromatography?
Volatile gas mix is inserted, mobile gas carries components through the machine, reaches capillary column ( liquid stationary phase), components react with the stationary phase, more soluble is slower to come out so will reach the detector last.
What is the separation of gas chromatography based on?
based on different solubilities in the stationary phase
What is retention time?
Time take for each sample to travel through the column
What can the peak areas be used to determine?
conc of components in the sample using a calibration curve
Test for alkenes?
decolourize bromine water (orange to colourless)
Test for haloalkane?
Add silver nitrate + ethanol
chloroalkane= white precipitate
bromoalkane= cream precipitate
iodoalkane= yellow precipitate
Test for carbonyl?
2,4 DNP= orange precipitate
Test for aldehyde?
Tollens reagent, a Silver mirror as silver is reduced and the aldehyde is oxidised
Test for primary, secondary alcohol + aldehyde?
add acidified potassium dichromate and warm
orange to green
Test for carboxylic acid?
add Na2CO3 (aq) effervescence
Test for phenol?
decolourize bromine + white precipitate
Why NMR is used?
map out carbon-hydrogen framework
How NMR works?
If Carbon is not surrounded by electrons, it feels a stronger magnetic field. more energy is required to spin-flip so a higher freq of radio waves is required to turn C into resonance
What is TMS?
The standard reference for chemical shift used in NMR
- 4 identical carbons produce a strong signal
- carbon is more electronegative than Si so is stronger shielded
only a low radio freq required
Why CDCL3 used as a solvent in NMR?
No Hydrogen atoms so do not interfere with H1 NMR and Carbon can be filtered
What is the chemical shift?
the shift in freq compared to TMS required for a nucleus to undergo resonance
What carbon 13 NMR shows?
- number of carbon environment= number of peaks
- types of carbon environments= chemical shift values
How to identify OH and NH peaks?
Proton NMR is run as normal
add D2O and sample is re-run
D exchanges and replaces OH and NH so their peak disappears
Compare to the original NMR
