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A short class with Sarah and her students. The other ways are under More.
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Here is CH3COOH. Which two familiar groups can you see on the last carbon?
A C=O, like in aldehydes and ketones, and an –OH, like in alcohols.
Right, and together they make the carboxyl group. So does acetic acid react like a ketone and like an alcohol?
I would guess yes, but you are smiling, so probably not.
Good instinct. A lone pair on the –OH oxygen is shared with the C=O group by resonance, so the carbon is less positive than in a ketone. That is why carboxylic acids do not add HCN the way aldehydes do.
So the two groups change each other. It is really a new group, not two old ones stuck together.
Exactly.
Name CH3CH(CH3)COOH.
The chain with the carboxyl carbon has three carbons, so it is propanoic acid. The methyl is on carbon 2, so 2-methylpropanoic acid.
Why didn't you number from the other end?
Because the carboxyl carbon is always carbon 1.
Perfect. Now try HOOC–CH2–COOH.
Three carbons and two carboxyl groups, so propanedioic acid. We keep the e of propane.
Correct. Its common name is malonic acid.
Ethanoic acid and propan-1-ol have the same molar mass. Which boils higher?
Both can hydrogen-bond, so maybe they boil at about the same temperature?
Ethanoic acid boils at about 118 °C and propan-1-ol at about 97 °C. Why the gap?
Two acid molecules can join through two hydrogen bonds at once and form a dimer, so they hold together more strongly.
Exactly. The C=O of one molecule accepts a hydrogen bond while its O–H donates one, so each molecule pairs neatly with a partner.
a C=O and an –OH on the same carbon; general formula R–COOH.
the carboxyl carbon is C-1 and the ending is -oic acid, or -carboxylic acid when the group is on a ring.
the –OH lone pair makes the carbon less electrophilic than in aldehydes and ketones.
two equivalent resonance structures share the negative charge, which explains the acidity.
dimers give acids higher boiling points than alcohols of similar molar mass.
CH3CH2CH(CH3)COOH is 2-methylbutanoic acid: number from the carboxyl carbon (C-1) along the four-carbon chain, with the methyl group on C-2.
HOOC–(CH2)4–COOH is hexanedioic acid, better known as adipic acid, which is used to make nylon-6,6.
Ethanoic acid (60 g/mol) boils at about 118 °C, higher than propan-1-ol (60 g/mol, about 97 °C), because acid molecules pair up as hydrogen-bonded dimers.
Carbon one is where the COOH sits; add -oic acid and the name fits.
Two ethanoic acid molecules at a dance always hold both hands, one hydrogen bond in each, and it takes a lot of heat to pull them apart.
Ants, Vinegar, Butter: formic acid from ants, acetic acid from vinegar, butyric acid from butter.
C.A.R.B. - Carboxyl carbon is C-1, Add -oic acid, Resonance shares the charge, Bonds to water make small acids soluble.
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IUPAC name of HCOOH
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Which carbon is C-1 in the name of a carboxylic acid?
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Suffix used when –COOH is attached directly to a ring
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Why are both C–O bonds equal in a carboxylate ion?
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IUPAC name of oxalic acid
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The –COOH group: a carbonyl group and a hydroxyl group on the same carbon atom.
An organic compound containing one or more carboxyl groups; general formula R–COOH.
The anion R–COO⁻ formed when a carboxylic acid loses a proton.
The spreading of electrons over several atoms, shown by two or more structures whose hybrid is the real molecule.
Two molecules joined together; here, two acid molecules held by two hydrogen bonds.
An acid with two carboxyl groups, such as ethanedioic (oxalic) acid.
A long-chain carboxylic acid found combined in fats and oils, such as stearic acid.
Carboxylic acids contain the carboxyl group, –COOH, in which a carbonyl group and a hydroxyl group share one carbon atom. This lesson covers how carboxylic acids are named and how the structure of the carboxyl group explains their behaviour.
A carboxylic acid has the general formula R–COOH. IUPAC names count the carboxyl carbon as C-1 and replace the final -e of the alkane with -oic acid, while many acids keep common names taken from their natural sources, such as formic acid from ants and acetic acid from vinegar. The carboxyl carbon is sp2 hybridised and planar; resonance with the –OH group makes it less electrophilic than the carbonyl carbon of aldehydes and ketones, and the resonance-stabilised carboxylate ion explains why these compounds are acids. Hydrogen bonding, including the pairing of molecules into dimers, gives carboxylic acids high boiling points and makes the smaller ones soluble in water.
The carboxyl group, –COOH, is made of a carbonyl group (C=O) and a hydroxyl group (–OH) on the same carbon atom; its name joins carb(onyl) and (hydr)oxyl. Compounds with one carboxyl group are monocarboxylic acids, R–COOH, where R is a hydrogen atom, an alkyl group or an aryl group. Saturated open-chain monocarboxylic acids have the general formula CnH2nO2. Acids with two carboxyl groups are dicarboxylic acids. Long-chain acids found combined in fats and oils, such as palmitic acid (C15H31COOH) and stearic acid (C17H35COOH), are called fatty acids.
Many acids are still known by names that recall where they were first found:
In common names, positions along the chain are shown by Greek letters: the carbon next to –COOH is α, the next β, then γ. So CH3CHClCOOH is α-chloropropionic acid in the common system.
The carboxyl group is therefore more than a carbonyl group and a hydroxyl group placed side by side: each changes the other. This single idea explains the naming pattern, the acidity, the high boiling points and the chemical reactions met later in the chapter.