Carboxylic acid derivatives: Intro + phy properties

What are carboxylic acid derivatives?

Compounds in which the -OH group in the carboxylic acid is replaced by -Y which can be -F, -Cl, -Br, -I, -OR’, -NH₂

general structure and nomenclature of acyl chloride

• replace ‘oic acid’ with ‘oyl chloride’ eg methanoyl chloride

general structure and nomenclature of an ester

• first R group attached to oxygen ends with ‘yl’

• followed by parent carboxylic acid replacing ‘oic acid’ with ‘oate’

• eg phenyl ethanoate

general structure of an amide

Acyl chlorides and esters have higher/lower boiling points than carboxylic acids. explain.

• lower

• less energy required to overcome the weaker permanent dipole-permanent dipole interactions as compared to stronger hydrogen bonding between carboxylic acid molecules

(no intermolecular hydrogen bonding as there is no hydrogen directly attached to highly electronegative oxygen)

Solubility of esters

• less soluble in water than carboxylic acids, may even be immiscible in water

• esters only have on C=O group to accept a H-bond whereas carboxylic acids have both a C=O group to accept a hydrogen bond and a O-H group to donate a hydrogen bond

• energy released from weaker hydrogen bonding between ester and water molecules

• is less able to /less than energy required to

• overcome the pd-pd interactions between ester molecules and hydrogen bonding between water moleculces

rank reactivity of the following carboxylic acid derivatives towards nucleophilic substitution

• carboxylic acid

• acyl chloride

• ester

• amide

amide < ester < carboxylic acid < acyl chloride

Why is acyl chloride most reactive in nucleophilic substitution?

electornic effects

• halogen substituent withdraws electrons through inductive effect from C=O group

• increasing partial positive charge on the carbon group

• making it more susceptible to nucleophilic attack

(compared to in carboxylic acids, the lone pairs on OH oxygen delocalise into the carbonyl pi orbital through resonance effect, neutralising the partial positive charge on carbonyl carbon)

leaving group

• halides are weaker bases, hence are better leaving groups

Why are amides and esters less reactive towards nucleophilic substitution?

• amino group or alkoxy group donates electrons to carbonyl carbon through resonance effect

• decreasing the partial positive charge on carbonyl carbon

• amides and esters are less readily attacked by nucleophiles

(nitrogen is less EN so donates more)

leaving group

• amino group adn alkoxy group are strong bases, hence are have a lower leaving group ability (amino group is a stronger base)

carboxylic acids and esters are ___ isomers if they have the same number of carbons

constitutional isomers