Question

The reaction between propinoyl chloride and acetate ion is outlined below. a) Complete the meachanism of the forward reation by placing curved arrows to show the electron movements in the reactants and intermediate product. b) Draw the structures of the final product and leaving group, including any charges. (Elecrons may be omitted.)

Answer 1

Concepts and reason

In the given reaction acid chloride reacts with acetate ion and an acid anhydride is formed. This reaction is a type of nucleophilic acyl substitution reaction in the which a nucleophile substitutes the substituent that was attached to acyl group in the reactant.

Fundamentals

The carboxylic acid and its derivatives undergo nucleophilic acyl substitution reaction. In this reaction, a nucleophile substitutes the substituent that was attached to acyl group in the reactant, that is, carboxylic acid and its derivatives. The reaction occurs because the carbonyl group is polar, thus, the carbonyl carbon gets a partial positive charge and oxygen atom gets a partial negative charge. The carbonyl carbon is attacked by nucleophiles.

The general reaction mechanism of nucleophilic acyl substitution reaction is as follows:

In the first step, the carbon of carbonyl is attacks by nucleophile and C-O bond is breaks. As the breaks, a tetrahedral intermediate is formed. In the second step, the negative charge presents in oxygen re-forms the and expelled the with its bonding electron.

In the second step, three groups are present, the group which is weaker base is the better leaving group.

(a)

The negative charge containing oxygen in acetate ion attacks the carbonyl carbon of acid chloride.

The reaction is as follows:

The tetrahedral intermediate reformed the double bond and by the removal of chloride ion.

The curved arrow reaction mechanism for the formation of product in the intermediate is as follows:

[Part a]

(b)

The product and the leaving group for the above reaction are as follows:

[Part b]

Ans: Part a

The curved arrow mechanism when acid chloride reacts with acetate ion and for the removal of chloride ion is as follows: