A bit of organic

very broadly, two types of isomerism

structural and stereoisomerism

Three types of structural isomerism

chain, positional and functional group

When/why do alkenes display geometrical isomerism

When there are two different substituents on each carbon atom forming the double bond. There is restricted rotation around the double bond, due to the sideways overlap of p orbitals in the pi bond.

Two ways alkanes can be produced

hydrogenation of alkenes (Pt or Ni catalyst, hydrogen gas, heat) or cracking of longer alkanes (aluminium oxide catalyst, 600-700 heat)

Three steps in free radical substitution (and how many of each)

• Initiation (1)

• Propagation (2)

• Termination (3 possible)

Why is a tertiary carbocation more stable than secondary or primary

It has more electron-pushing alkyl groups, so the positive charge is more spread out

Alkene reaction with cold, dilute, acidified potassium permanganate

forms diol

alkene reaction with hot, concentrated, acidified potassium permanganate

• If two hydrogens: carbon dioxide via methanoic acid

• If two R groups: ketone

• If one R group and one hydrogen: carboxylic acid

Can you have geometrical isomerism in a cyclic compound

NO - switching the position of two groups would break the ring, so it is not possible

Environmental consequence of unburnt hydrocarbons

React with oxides of nitrogen (specifically NO2) to produce PAN, which produces photochemical smog

Which two harmful products of incomplete combustion in car engines can react together to remove them both

NO + CO —> ½ N2 and CO2

How to test which halogen is present in a halogenoalkane

First substitution: aqueous NaOH and heat - forms an alcohol and the halide ion

Acidify: add aqueous nitric acid

Test: add aqueous silver nitrate - white ppt: chlorine; cream ppt: bromine, yellow ppt: iodine

Test: add dilute ammonia: AgCl will dissolve; add conc. ammonia: AgBr will dissolve

Different reactivities of halogenoalkanes

Iodoalkane > bromoalkane > chloroalkane. The C-I bond is the weakest (due to shielding), so the bond enthalpy is the lowest.

How to identify an alcohol

Acidified K2Cr2O7 solution changes colour from orange to green

methyl alcohol + alkaline I2 (aq)

Yellow ppt of triiodomethane (CHI3) and carboxylate ion

acidity of alcohols compared to water

Alcohols are less acidic than water, because they have alkyl groups, which have a positive inductive effect - this pushes the electrons onto the oxygen in the alcoxide ion, making it more negative, so it is more likely to react with a hydrogen ion to form the alcohol again.

2,4-DNPH with carbonyl

Orange ppt

Fehling’s with ketone vs aldehyde

Aldehyde: blue —> red ppt. Ketone: nothing

Tollen’s with ketone vs aldehyde

aldehyde: silver mirror, ketone: nothing

methyl carbonyl with alkaline I2(aq)

yellow ppt of triiodomethane and carboxylate ion

Why is it difficult to dispose of polyalkenes

they are inert and non-biodegradable, and form harmful products when combusted

Difference between any two enantiomers

the direction that they rotate plane polarised light in

how do you separate one enantiomer from a racemic mixture

by using a chiral catalyst

which substituents are 2,4,6 directing

Alkyl, OH in phenol, NH2 in phenylamine

which substituents are 3,5 directing

NO2, carbonyl, carboxylic acid

Does freidel-crafts use heat

YES

Difference in reactivity between a halogenoalkane and a halogenoarene

Halogenoarenes are much less reactive than halogenoalkanes. This is because a lone pair on the halogen can partially delocalise into the benzene ring, which makes the carbon-halogen bond stronger. Nucleophiles are also repelled by the benzene ring.

Relative acidities of water, phenol and ethanol

Phenol > water > ethanol. Lone pair on the oxygen in phenol can be partially delocalised within the benzene ring, drawing electron density away from the oxygen so weakening the O-H bond, making it easier to form H+ ions. In ethanol, the electron-pushing ethyl group strengthens the O-H bond as it increases the electron density on the oxygen, making it harder to donate a proton.

Why are the reagents and conditions for the nitration and bromination of phenol different from those for benzene

Phenol is more reactive than benzene, as a lone pair on the oxygen can partially delocalise into the ring, which gives it a greater electron density. This means that it is more nucleophilic and more strongly attracted to an electrophile.

relative acidities of carboxylic acids, phenols and alcohols

carboxylic acid > phenol > alcohol. Carboxylic acid the strongest as the C=O has an electron withdrawing effect and weakens the O-H bond, making it easier to lose H+. Phenol stronger than ethanol as a lone pair on the oxygen can be partially delocalised into the ring, which weakens the O-H bond. Ethanol the weakest as the ethyl group has a positive inductive effect, and strengthens the O-H bond. (Can also say how all of these things (de)stabilise the anion)

relative acidities of chlorine-substituted carboxylic acids

the more Cl atoms, the stronger the acid, since the Cl atoms have an electron-withdrawing effect, which weakens the O-H bond, and makes it easier to lose H+.

what conditions are needed for any addition-elimination

rtp

basicity of aqueous solutions of amines

Lone pair on the nitrogen can accept protons. The more alkyl groups, the more basic, as they have positive inductive effects and push electrons onto the N atom, making it more negative.

relative basicities of ammonia, ethylamine and phenylamine

Ethylamine > ammonia > phenylamine. Ethylamine most basic as the ethyl group is has a positive inductive effect, so pushes electrons onto the N atom, increasing the electron density so making the lone pair more available to form a dative covalent bond. Phenylamine least basic as the lone pair on the N atom can partially delocalise into the benzene ring, so it is less available for dative bonding.

Why are amides much weaker bases than amines

The electron-withdrawing oxygen removes electron density from the nitrogen atom, which means that its lone pair is less available to a proton

When does SN1 occur vs SN2

SN1 occurs with tertiary halogenoalkanes, as it forms a tertiary carbocation intermediate, which is more stable than a primary carbocation, since it has more alkyl groups which have a positive inductive effect; and steric hindrance from the alkyl groups prevents nucleophilic attack. SN2 occurs with primary halogenoalkanes, since there is less steric hindrance as there are fewer alkyl groups, and the carbocation intermediate would be less stable.

What is formed in SN2 before the products

a TRANSITION STATE (not intermediate)