Question

What is the major organic product? i)(CH3)₂ Culi 2) H3O+ Prediet final product i) sodium ethoxide in sodium ethoxide Hot 2) I-bromopentane 2) bromomethane a) 2-methylpentanoic acid cethul z-methylheptanoate b) 2-methul hept anoic acid d) 3-methylhexanoic acid

Answer 1

In these reactions, there are two possibilities.

(1) directly attacking the carbonyl( 1,2 addition )

(2) attacking the alkene(1,4 addition).

OH Hu Nu > H+ H तेर 2 Ümu Nu ų I Tautomerise O-H Nu

Above are the two mechanisms possible. See that I have labelled the atom in the reactant, which says why the first reaction is 1,2 addition and the second one 1,1 addition.

Now how to say that where the nucleophile will attack?

Whether 1,2 or 1,4-addition occurs depends on multiple variables but mostly it is determined by the nature of the nucleophile. During the addition of a nucleophile, there is a competition between 1,2 and 1,4 addition products. If the nucleophile is a strong base, such as Grignard reagents, both the 1,2 and 1,4 reactions are irreversible and therefore are under kinetic control. Since 1,2-additions to the carbonyl group are fast, we would expect to find a predominance of 1,2-products from these reactions.

If the nucleophile is a weak base, such as alcohols or amines, then the 1,2 addition is usually reversible. This means the competition between 1,2 and 1,4 addition is under thermodynamic control. In this case, 1,4-addition dominates because the stable carbonyl group is retained.

Organolithium reagents react with cuprous iodide to give a lithium dimethylcopper reagent( (CH₃)₂CuLi ), which is referred to as a Gilman reagent. Gilman reagents are a source of carbanions like nucleophiles similar to Grignard and Organolithium reagents. However, the reactivity of organocuprate reagents is slightly different and this difference will be exploited in different situations. In the case of α, β unsaturated carbonyls organocuprate reagents allow for a 1,4 addition of an alkyl group.

Hence, here, 1,4 addition will occur and the product is:

Oh