(a) the use of C–C bond formation in synthesis to increase the length of a Carbon chain
(see also 6.1.1 d, 6.1.2 b)
(b) formation of C-CN by reaction of:
(i) Haloalkanes with CN– and Ethanol, including nucleophilic substitution mechanism
(see also 4.2.2 c)
(ii) Carbonyl compounds with HCN, including nucleophilic addition mechanism
(see also 6.1.2 b–c)
Clearly, there will be times when your reactants are not exactly the same length as your desired product.
So you'll need to find ways to make alkyl chains longer.
These have been covered in the sections mentioned on the syllabus above.
So, there's not much point repeating them
You can go straight to the relevant sections by clicking the links below;