Unit 4 return of the organic chemistry Flashcards
Saturated
Contain single carbon-carbon bonds only
Unsaturated
Contains a C=C double bond
Molecular formula
The formula which shows the actual number of each type of atom
what are Homologous series
are families of organic compounds with the same functional group and same general formula.
•They show a gradual change in physical properties (e.g. boiling point).
• Each member differs by CH2
from the last.
• same chemical properties.
Functional group
is an atom or group of atoms which when present in different molecules
causes them to have similar chemical properties.
what is the functional group of an alcohol?
A carbon bonded to a OH.
What is the functional group of an aldehyde?
A carbon double bonded to oxygen, single bond to hydrogen, one more bond.
What is the functional group of a ketone.
A carbon double bonded to an oxygen with 2 spare bonds.
What is the functional group of a carboxylic acid?
carbon double bonded to oxygen, single bond to OH, one spare bond.
What is the functional group of nitriles?
carbon triple bonded to nitrogen with one spare bond.
What is the functional group of amines?
carbon boned to NH2 with 3 spare bonds.
what is the functional group for esters?
A carbon double bonded to an oxygen. one spare bond and one to an oxygen which also has one spare bond.
what is the functional group for amides?
A carbon double bonded to an oxygen, and a NH2 whith one spare bond.
Structural isomers
same molecular formula different structures (or structural formulae)
Chain isomers
Compounds with the same molecular formula but different structures of the carbon skeleton
position isomers
Compounds with the same molecular formula but different structures due to
different positions of the same functional group on the same carbon skeleton
Functional group isomers
Compounds with the same molecular formula but with atoms arranges to give different
functional groups
Stereoisomerism
have the same structural formulae
but have a different spatial arrangement of atoms
what are the 2 types of stereo-isomerism?
geometrical (E- Z isomerism) and optical
isomerism
why do E/Z isomers exist?
restricted rotation about the C=C bond
how is priority chosen when deciding on E/Z isomers?
the one with the larger Ar gets priority.
when does optical isomerisation occur?
Optical isomerism occurs in carbon compounds with 4
different groups of atoms attached to a carbon (called
an asymmetric carbon).
If a carbon atom has four different groups attached to it, what is it called?
a chiral (asymmetric) carbon atom
how does optical isomerisation occur?
The 4 different groups are the mirror images of each other. They will have similar chemical and physical property’s but will rotate light in different directions by the same amount.
What are enantioemers?
Two compounds that are optical isomers of
each other
what is a racemate mixture?
A mixture containing a 50/50 mixture of the two isomers (enantiomers)
what will a positive enantioemer do to light?
Rotate clockwise. This is dextrorotatory
what will a negative enantioemer do to light?
Rotate anticlockwise. laevorotatory
What will a racemate mixture do to polarised light?
Nothing.
How do racemates form?
A racemate will be formed in a reaction
mechanism when a trigonal planar reactant or
intermediate is approached from both sides by
an attacking species
how does HCN form a racemate when reacting with an aldehyde or ketone.
The NC: nucleophile can attack on either sides of the C=O bond. It will be 50/50 and will produce a racemate.
How does the SN1 mechanism produce a racemate?
Something will come off, like a Br to produce a carbocation intermidate. (carbon with a + where the bond was).
The negative nucleophile can then join from other sides.
How does the SN2 mechanism produce an optical isomer?
A transition state will occour with the nucleophile joining before anything has left. The product will rotate light in a different direction to the reactant, though it won’t give a racemate.
How is a ketone with two c=o named?
di is put before –one and an e is added to the stem
e.g. Pentane-2,4-dione
How will a double ended carboxylic acid get named?
It becomes a dioic acid like Ethanedioic acid
How are esters named?
The bit ending in –yl comes from the alcohol that has
formed it and is next to the single bonded oxygen.
The bit ending in –anoate comes from the carboxylic acid. (This is the chain including the C=O bond
e.g. Methyl propanoate
How are Acyl Chlorides named?
add –oyl chloride to the stem name
What is a Carbonyls compound?
Carbonyls are compounds with a C=O bond.
They can be either aldehydes or ketones
What is the solubility of Carbonyls in water?
The smaller carbonyls are soluble in water because they can form hydrogen bonds with water.
How do pure carbonyls bond to each other?
Pure carbonyls cannot hydrogen bond, but
bond instead by permanent dipole bonding.
How does the C=O bond determine reactions for carbonyls?
The C=O bond is polarised because O is more electronegative than carbon. The positive carbon atom attracts nucleophiles.
Compare the bond strength of C=C and C=O.
In comparison to the C=C bond in
alkenes, the C=O is stronger and does
not undergo addition reactions easily.
formula for potassium dichromate.
K2Cr2O7
What agent is potassium dichromate?
oxidising agent
what do primary alcohols oxidise to?
Primary alcohol> aldehydes > carboxylic acid
How is an aldehyde oxidised?
Reaction: aldehyde > carboxylic acid
Reagent: potassium dichromate (VI) solution and
conc sulphuric acid.
Conditions: heat under reflux
What is observed when using dichromate to oxidise an aldehyde?
the orange dichromate ion(Cr2O7 2-) reduces to the green Cr 3+ ion
What is the equation when using dichromate to oxidise an aldehyde?
3CH₃CHO + Cr₂O₇²⁻+ 8H⁺ = 3CH₃CO₂H + 4H₂O + 2Cr³+
How is Tollen’s reagent used?
Reagent: Tollen’s Reagent formed by mixing
aqueous ammonia and silver nitrate. The
active substance is the complex ion of [Ag(NH₃)₂]⁺
Conditions: heat gently
Reaction: aldehydes only are oxidised by
Tollen’s reagent into a carboxylic acid and
the silver(I) ions are reduced to silver atoms
Observation: with aldehydes, a silver mirror forms
coating the inside of the test tube. Ketones
result in no change.
It is an oxidising agent.
Fehling’s solution
Containing blue Cu 2+ ions dissolved in sodium hydroxide.
Conditions: heat gently
Reaction: aldehydes only are oxidised by Fehling’s
Solution into a carboxylic acid and the copper ions
are reduced to copper(I) oxide . .
Observation: Aldehydes :Blue Cu 2+ ions in solution
change to a red precipitate of Cu2O. Ketones do
not react.
oxidising agent.
equation of Tollen’s reacting with ethanal
CH3CHO + 2Ag⁺ + H2O CH3COOH + 2Ag + 2H⁺
equation of Fehling’s solution reacting with ethanal
CH3CHO + 2Cu²⁺ + 2H₂O CH3COOH + Cu2O + 4H+
what will reduce carbonyls?
Reducing agents such as NaBH4 (sodium tetrahydridoborate) or LiAlH4 (lithium tetrahydridoaluminate) will reduce carbonyls to alcohols.
What are the reagents and conditions for reduction of carbonyls?
LiAlH4 In dry ether. Room temperature and pressure
what are aldehydes reduced to?
Primary alcohols.
what are ketones reduced to?
secondary alcohol.
Addition of hydrogen cyanide to carbonyls to form hydroxynitriles
Reaction: carbonyl hydroxynitrile
Reagent: HCN in presence of KCN
Conditions: Room temperature and pressure
Mechanism: nucleophilic addition
When HCN is added to an aldehyde, what is the structure of the product?
The OH is replaced with a carbon. Bonded to this is H, OH and C then N.
When HCN is added to a ketone, what is the structure of the product?
The carbon double bonded to the C=O will lose the O and a OH and CN will add to both sides.
Why, when reacting with HCN, is KCN also present?
The extra KCN increases the concentration of the CN ion nucleophile needed for the first step of the mechanism
What is the mechanism for the reaction of carboyls with HCN?
The HCN forms :CN⁻. This will donate electrons to the sigma positive carbon in C=O and the double bond will donate 2 electrons to the O to make :O⁻ which remains attached. The CN joins.
The oxygen then donates the 2 electrons to the H of a new H-CN. The CN then gains 2 electrons from the H-CN bond and leave and the H will bond with the oxygen.
Reaction of carbonyls with iodine in presence of alkali
Iodine and sodium hydroxide. Gently warm.
product of the iodoform test?
The product CHI3 is a yellow crystalline precipitate, smells antiseptic.
Water, NaI and RCOONa are also given
RCOONa is C double bonded to O and O-Na+
What is the reaction of the iodoform test?
I₂ and NaOH will react with the carbonyl to give iodoform, NaI, water and the carbonyl having a COONa.
what is the proper name of brady’s?
2,4-dinitro phenylhydrazine
What is the structure of brady’s?
:NH₂NH connected to a benzene ring with NO₂ in the 2 and 4 position.
How can the precipitate produced by Brady’s get used to determine the chemical is reacted with?
You measure the melting point and compare it to known values.
Describe the solubility of carboxylic acid in water.
The smaller carboxylic (up to C4) acids dissolve in water in all proportions but after this the solubility rapidly reduces. They dissolve because they can hydrogen bond to the water molecules.
What are carboxylic acid salts stabilized by?
The carboxylic acid salts are stabilised by delocalisation,
which makes the dissociation more likely.
The OH loses the H and C=O becomes a C-O. Electrons are delocalised around the O-C-O meaning it is more stable and more likely to form.
How is a carboxylic acid produced from a primary alcohol?
Reaction: primary alcohol >carboxylic acid
Reagent: potassium dichromate(VI) solution and dilute sulphuric acid
Conditions: use an excess of dichromate, and heat under reflux: (distill off product after the reaction has finished)
They are fully oxidised.
How can nitriles (contains C triple bond N) get turned to carboxylic acids?
They are hydrolysed. Reflux with dilute HCl and water.
Give the equation of Propionitrile get hydrolyzed to carboxylic acid.
CH3CH2CN + HCl+ 2H₂O > CH3CH2COOH + NH4Cl
What are carboxylic acids reduced to ?
Use LiAlH4 to reduce straight to primary alcohol. Water also given
How are carboxylic acids reduced?
Reagents: LiAlH4 In dry ether
Conditions: Room temperature and pressure
Type of reaction: Reduction
Role of reagent: Reducing agent
What are the different ways in which a carboxylic acid can produce a salt?
acid + metal (Na) >salt + hydrogen
acid + alkali (NaOH) >salt + water
acid + carbonate (Na2CO3) >salt + water + CO2
What is the only carboxylic acid that can be oxidised?
methanoic acid is an
exception as its structure has effectively an
aldehyde group. A O will be go between C and H in the C-H bond.
Describe the reaction of carboxylic acid with phosphorous (V) chloride
Reaction: carboxylic acid acyl chloride
Reagent: PCl5 phosphorous(v)chloride
Conditions: room temp
HCl, POCl3 and acid chloride are given.
describe the esterfication of carboxylic acid.
Carboxylic acids react with alcohols, in the
presence of a strong acid catalyst, to form
esters and water.
The reaction is reversible and slow. It needs to be refluxed with an acid catalyst (sulphuric acid)
What are some of the uses of esters?
Esters are sweet smelling compounds that can be used in
perfumes and flavourings. For use in perfumes they need to be non toxic, soluble in solvent such as ethanol, volatile (turns into gas easily), and not react with water.
Esters can be used as solvents for polar organic substances
Do esters form hydrogen bonds and how does this affect their physical properties?
Although polar, they do not form hydrogen bonds (reason: there is no hydrogen bonded to a highly electronegative atom) thus, they have much lower b.p. than the hydrogen-bonded carboxylic acids they came from. They are also almost insoluble in water.
What are the two ways to hydrolysis esters?
Esters can be hydrolysed and split up by either heating with acid or with sodium hydroxide.
Describe the hydrolysis of an ester with an acid.
Heat under reflux with dilute acid (HCl)
This reaction is the reverse reaction of ester formation.
Ester reacts with water and it split to give alcohol and carboxylic acid.
Describe the hydrolysis of an ester with a base.
reagents: dilute sodium hydroxide
conditions: heat under reflux
Reacts with OH- to give alcohol and carboxylic ion
The anion is resistant to attack by weak nucleophiles such as alcohols, so the reaction is not reversible.
Describe the hydrolysis of methyl propanoate with a base.
sodium propanoate and methanol is produced.
What is the structure of sodium propanoate?
It is like propanoic acid but the OH is O⁻Na⁺
What are the derivatives of carboxylic acids?
Acyl Chlorides and Acid Anhydrides
Why are the derivatives of carboxylic acids more reactive?
The Cl group is classed as a good leaving
groups (to do with less effective delocalisation.)
This makes acyl chlorides and acid anhydrides
much more reactive than carboxylic acids and
esters
acid chloride with water.
Carboxylic acid and HCl produced.
RCOCl (l) + H2O >RCO2H + HCl (g)
Acid chloride and alcohol.
Ester and HCl produced.
RCOCl (l) + CH3CH2OH > RCO2CH2CH3 + HCl (g)
This reaction for making esters is much better than using
carboxylic acids as the reaction is much quicker and it is
not a reversible reaction
Acid chloride and ammonia.
Change in functional group: acyl chloride primary amide Reagent: ammonia Conditions: room temp. RCOCl (l) +2NH₃ RCONH2 + NH4Cl
Acid chloride and primary amines.
Change in functional group: acyl chloride secondary amide Reagent: primary amine Conditions: room temp. RCOCl +2CH3NH2 RCONHCH3 + CH3NH3⁺Cl⁻
There are two types of polymerisation=
addition and condensation
Condensation Polymerisation
In condensation polymerisation there are two different monomers that add together and a small molecule is usually given off as a side-product e.g. H2O or HCl.
What is the ion in tollens that causes it to react and how does it do so?
[Ag(NH₃)₂]⁺
[Ag(NH₃)₂]⁺ +e- = Ag + 2NH3. The silver is what you see.
When Brady’s reacts with a carbonyl, what is formed?
the double bond of the C=O will bond to the :HH2.
The H2 and the oxygen will come off to give water.
What is benedict’s solution?
Same as Fehling’s but the copper ions are dissolved in sodium carbonate, not sodium hydroxide.
When you reduce a carbonyl, what reaction is it?
Nucleophilic addition reactions. The reducing agent provides a H- to attack the σ+ carbon.
What is the iodoform test a test of?
a carbony group bonded to CH3 with one spare bond.
What is a dimmer?
When a carboxylic acid hydrogen bonds to one other molecule and effectively doubles the size of the molecule.
What is transesterification?
Reacting an alcohol with an ester to get a new alcohol and ester out. The latter part of the ester’s name will change.
How is biodiesel produced?
Fats and oils are reacted with methanol or ethanol to give methyl or ethyl esters
triglyceride + methanol = glycerol + methyl ester
what do you need to form terylene (PET)?
benzene-1,4-dicarboxylic acid and ethane 1,2-diol
what is the structure of benzene-1,4-dicarboxylic?
Carbon bonded to OH and double bonded to O. One of these on opposite sides of a benzene ring
How is PET formed?
benzene-1,4-dicarboxylic loses one OH and the other OH loses a H.
The same happens to ethane 1,2-diol.
They are then connected by O between them. Water is also given.
What is the general equation for the iodoform test
RCOCH₃ +3I₂ + 4NaOH → CHI₃ + RCOONa + 3NaI + 3H₂O
How can a carboxylic acid form from a nitrile ?
Reaction: (acid) hydrolysis
Reflux with HCl for carboxylic acid and ammonium chloride (NH4Cl)
What are vegetable oils and animal fats?
Triesters. They contain 3 ester groups.
How are vegetable oils and animal fats made?
Trans-Esterification of glycerol (Propane -1,2,3-triol) with fatty acids (long chain carboxylic acids)
Each OH is replaced with a fatty acid joined by an ester bond.
How do you form a soap?
Hydrolyse fats and oils by heating with concentrated NaOH and allow to cool.
Add NaCl solution and the soap will separate out as the crust on top
What is chiral molecule?
A chiral molecule is non-superimposable on its mirror image / 3D molecule with no plane of symmetry
