How are these questions tested in the A level syllabus? There seems to be little emphasis on this section of the notes and tutorials.
Originally posted by a mugger:How are these questions tested in the A level syllabus? There seems to be little emphasis on this section of the notes and tutorials.
If you're asking literally "what kind of qns do they ask about alkyl halides", then your answer lies in the TYS.
If you're asking for advice on how to approach alkyl halides, then :
Appreciate that alkyl halides are electrophiles (girls), because they have very good leaving groups (old boyfriends), and hence can be attacked by nucleophiles (new boyfriends).
Halogens are good leaving groups because halide ions are stable, because they have low anionic charge densities. The only exception, of course, is F : F is a poor leaving group because F- has a high anionic charge density. Additionally the C-F bond dissociation enthalpy is significantly more endothermic than the other C-X bond dissociation enthalpies.
On this topic, you should also appreciate how the two factors "sterics" and "electronics" collectively determine why primary alkyl halides undergo SN2, why tertiary alkyl halides undergo SN1, and why secondary alkyl halides undergo both.
For the H2 syllabus, the emphasis is on synthesis : Alkanes are used to generate alkyl halides (via free radical substitution), which are then used as electrophiles to generate other species, such as alcohols.
If you wondering about "industrial uses of alkanes" ala O level syllabus, there is less of that in the H2 syllabus, but you still need to memorize a small section on "hydrocarbons as fuels", including :
internal combustion engine
petrol additives
environmental consequences
catalytic converters
It's only a small section, and the main emphasis is on synthesis and mechanism, in regard to alkanes and alkyl halides.