Reactivity/physical properties for exam 3

Thiols reactivity

weak acids, do NOT form hydrogen bonds because the sulfur atom is not sufficiently electronegative

Physical Properties of Thiols compared to Alcohols

thiols are sulfur analogs of alcohols; -SH is mercapto group

Physical Properties of Sulfides compared to Ether

sulfur is much more nucleophilci than oxygen analogs, sulfides are easily oxidized

Which is generally more reactive — aldehydes or ketones?

Aldehydes are more reactive toward nucleophilic addition than ketones.

Why are aldehydes more reactive than ketones (steric reason)?

Aldehydes have only one alkyl group (or hydrogen), causing less steric hindrance around the carbonyl carbon.

Why are aldehydes more reactive than ketones (electronic reason)?

Aldehydes have fewer electron-donating groups, so their carbonyl carbon is more δ⁺ and electrophilic.

How do alkyl groups affect the reactivity of a carbonyl compound?

Alkyl groups donate electrons inductively, reducing the positive character of the carbonyl carbon and lowering reactivity.

Rank the following by reactivity toward nucleophilic addition: Formaldehyde, Aldehyde (RCHO), Ketone (R₂CO).

Formaldehyde > Aldehydes > Ketones.

Why is formaldehyde the most reactive carbonyl compound?

It has no alkyl groups, giving minimal steric hindrance and maximum positive charge on the carbonyl carbon.

How do electron-withdrawing groups affect carbonyl reactivity?

They increase reactivity by making the carbonyl carbon more electrophilic.

How do electron-donating groups affect carbonyl reactivity?

They decrease reactivity by stabilizing the carbonyl carbon and reducing its δ⁺ charge.

hybridization of carboxyl carbon

sp^2 hybridized

pH of carboxylic acids

acidic

acid strength of carboxylic acids

weaker than mineral acids, but stronger than alcohols and phenols

substituent effects on acidity with carboxylic acids

atoms that are bonded to carboxylate anions that have high electron-withdrawing capabilities make the carbon more acidic (more stable = more acidic)

effect of halogen substitution

effect decreases as the substituent moves farther from carboxyl (closer substituent is to carboxylic acid, the more acidic it is)

aromatic ring acidity

Aromatic rings with electron-donating groups are activated toward further electrophilic substitution, and aromatic rings with electron-withdrawing groups are deactivated ; deactivating groups make stronger acids and activating groups make weaker acids

relative reactivity of carboxylic acid derivatives

Reactivity increases as steric hindrance decreases; things with more hydrogens are less sterically hindered, increasing the reactivity