Pop-Quiz Sit down quietly and draw the following structures.

Pop-Quiz Draw the following structures: Heptan-2-ol Cyclopropanal 1-propoxypentane Heptan-3-one 2,4,6-trichloroheltanal

Nomeclature: Carboxylic acids and Esters

Structure of carboxylic acids and their derivatives The functional group present in a carboxylic acid is a combination of a carbonyl group and a hydroxyl group; however, the resulting carboxyl group ( -COOH) possesses properties that are unlike those present in aldehydes/ketones and alcohols.

Structure of carboxylic acids and their derivatives Carboxylic acids have the following general formula: Some simple carboxylic acids: Since carbon can have only four bonds, there are no cyclic carboxylic acids (i.e. the carboxyl group cannot form part of a carbon ring)

IUPAC nomenclature for carboxylic acids For monocarboxylic acids (one –COOH group): Select the longest, continuous carbon chain that involves the carboxyl group. This is the parent chain and the –COOH carbon is designated as C-1. Name the parent chain by dropping the “e” from the corresponding alkane name and changing to “oic acid” Indicate the identity and location of substituents on the parent chain at the front of the carboxylic acid’s name Benzoic acid

IUPAC nomenclature for carboxylic acids Dicarboxylic acids: For these compounds, both ends of a chain will end with a –COOH group. The parent chain is the one that involves both –COOH groups. The parent chain is named as an alkane and the term “dioic acid” is added afterwards to indicate the diacid structure.

Common names for carboxylic acids

Common names for dicarboxylic acids

Common names for carboxylic acids For common-name carboxylic acids and diacids, substituents are often numbered using a Greek system: So the following molecule is called 2-Methylpropanoic acid.

Polyfunctional carboxylic acids Carboxylic acids that contain other functional groups besides the –COOH group are called polyfunctional carboxylic acids. Some examples are shown below:

Task 2 Give IUPAC names for the following: A. CH3COOH CH3 | B. CH3CHCOOH

Solution 2 A. CH3COOH ethanoic acid CH3 | B. CH3CHCOOH 2-methylpropanoic acid;

Physical properties of carboxylic acids Carboxylic acids are the most polar functional group we have seen so far. The presence of the carbonyl group next to the OH causes the O-H bond to be even more polar.

Physical properties of carboxylic acids Because of the very polar –COOH group, carboxylic acids exhibit strong intermolecular attractions. As expected, carboxylic acids of a given number of carbon atoms have higher boiling points than alcohols. Carboxylic acids also tend to dimerize, producing molecules that are twice as heavy which have enhanced London forces (and thus still higher boiling points).

Comparing Boiling Points

Physical properties of carboxylic acids In terms of water-solubility, because of H-bonding, carboxylic acids dissolve well in water (up to 4-carbon chains). Beyond 4 carbons, water-solubility drops off rapidly.

Structure of esters Esters are carboxylic acid derivatives having an alkoxy group instead of a hydroxyl group.

Nomenclature for esters Thinking of an ester in terms of an “alcohol portion” and a “carboxylic acid portion” is important for naming esters using the IUPAC system: The name for the alcohol portion comes first: name the alkyl part of the alcohol (e.g., for the ester shown below, the first part of the ester’s name is methyl (alcohol part comes from methanol). Present the alkyl name separate from the remainder of the ester name. The carboxylic acid portion is named as if it were deprotonated, changing the “-ic acid” part of that name to “-ate” Methyl propanoate This part would be called “propanoate”

Nomenclature for esters Some other examples: Ethyl butanoate b g a Ethyl 2-methylbutanoate Ethyl a-methylbutyrate 2-Methylpropyl butanoate Isobutyl butanoate 2-Butyl butanoate Sec-Butyl butanoate

Selected common esters Flavor/fragrance agents

Selected common esters Pheromones: Medications:

Selected common esters Synthesis of Aspirin Synthesis of oil of wintergreen:

Task 2 Give the IUPAC name of the following compound, which is responsible for the flavor and odor of pears. O  CH3 — C—O —CH2CH2CH3

Solution 2 O  propyl CH3 — C—O —CH2CH2CH3 propyl ethanoate (IUPAC)

Isomerism in carboxylic acids and esters Recall that structural isomers are molecules that share the same formula but differ in their atom-to-atom connectivities. Carboxylic acids and esters that have a given number of carbon atoms form another example of functional group isomers:

Physical properties of esters Because they don’t possess OH groups, esters cannot form H-bonds with other ester molecules. As a result, esters have lower boiling points than carboxylic acids and alcohols that have approximately the same molar mass. Water molecules can H-bond to esters, at the oxygen atoms. This makes low molecule weight esters water-soluble.

Task 3 Draw the structure of the following compounds: 3-bromobutanoic acid Ethyl propionoate

Solution 3 A. 3-bromobutanoic acid Br | CH3CHCH2COOH B. Ethyl propionoate O  CH3 CH2 COCH2CH3 CH3CH2COOCH2CH3