In each part, rank the compounds in order of increasing rate of nucleophilic attack at C=O by a strong nucleophile like methoxide.
(b)

Verified step by step guidance

1. Step 1: Identify the functional groups attached to the carbonyl (C=O) in each compound. Compound E and F are amides (R-C=O-NH2), compound G is an ester (R-C=O-O-R'), and compound H is an anhydride (R-C=O-O-C=O-R').
2. Step 2: Understand the electronic effects of the functional groups. Amides (E and F) have resonance stabilization due to the lone pair on nitrogen, which reduces the electrophilicity of the carbonyl carbon. Esters (G) have less resonance stabilization compared to amides, making the carbonyl carbon more electrophilic. Anhydrides (H) are highly reactive due to the presence of two carbonyl groups, which increase the electrophilicity of the carbonyl carbon.
3. Step 3: Consider steric hindrance. Compound E has bulky alkyl groups near the carbonyl carbon, which can hinder nucleophilic attack. Compound F has less steric hindrance compared to E. Compound G has moderate steric hindrance due to the alkyl group attached to the oxygen. Compound H has minimal steric hindrance.
4. Step 4: Rank the compounds based on the combined effects of resonance stabilization, steric hindrance, and electrophilicity. Amides (E and F) will have the slowest rate of nucleophilic attack due to resonance stabilization, with E being slower than F due to steric hindrance. Esters (G) will have a faster rate than amides due to reduced resonance stabilization. Anhydrides (H) will have the fastest rate due to high electrophilicity and minimal steric hindrance.
5. Step 5: Final ranking in order of increasing rate of nucleophilic attack: E < F < G < H.

Key Concepts

Nucleophilicity

Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile, such as a carbonyl carbon in a C=O bond. Strong nucleophiles, like methoxide, are more reactive and can effectively attack electrophilic centers. The strength of a nucleophile is influenced by factors such as charge, electronegativity, and steric hindrance.

Electrophilicity of Carbonyl Compounds

The electrophilicity of carbonyl compounds is determined by the nature of the substituents attached to the carbonyl carbon. Electron-withdrawing groups increase the positive character of the carbonyl carbon, making it more susceptible to nucleophilic attack. Conversely, electron-donating groups can decrease electrophilicity, affecting the rate of reaction with nucleophiles.

Steric Hindrance

Steric hindrance refers to the repulsion between atoms that occurs when they are brought close together, which can impede reactions. In the context of nucleophilic attack on carbonyl compounds, bulky substituents around the carbonyl can hinder the approach of nucleophiles, thus affecting the reaction rate. Understanding steric effects is crucial for predicting the reactivity of different carboxylic acid derivatives.