3.20 Thiols Contain the functional group -SH Chp 3.20 3.20 Thiols Contain the functional group -SH Named by adding thiol to the name of the longest carbon chain Number the -SH group in longer chains CH3-SH methanethiol CH3-CH2SH ethanethiol SH CH3-CH-CH3 2-propanethiol

Thiols (cont.) and 3-methyl-1-butanethiol Many thiols have disagreeable odors Used to detect gas leak Found in onions, oysters, garlic and oysters Onions CH3CH2CH2-SH 1-propanethiol Garlic CH2= CHCH2-SH 2-propene-1-thiol Skunk spray CH3 trans-2-butene-1-thiol CH = CH CH2SH and 3-methyl-1-butanethiol

The oxidized product is called a disulfide. Oxidation of Thiols Thiols also undergo oxidation by a loss of hydrogen atoms from the –SH groups. The oxidized product is called a disulfide. [O] R1—S—H + H—S—R2 R1—S—S—R2 + H2O

Much of the protein in the hair is cross-linked by disulfide, which occur between the thiol groups of the amino acid cysteine. When a person is given a “perm”, a reducing substance is used to break the disulfide bonds. While the hair is still wrapped around the curlers, an oxidizing substance is applied that cause new disulfide bonds to form between different parts of the person hair strands, which gives the hair a new shape. COOH COOH COOH COOH [O] NH2—CH—CH2SH + HSCH2—CH—NH NH2—CH—CH2—S—S—CH2—CH—NH2 Cysteine