64. our hair maintains its shape because the fibers of keratin that make up the

Question

64. our hair maintains its shape because the fibers of keratin that make up the hair are bound with S-s (disulfide) bonds. The disulfide bonds are prone to reduction, and are converted into thiols. Oxidation of thiols converts them back to disulfides. How do you apply chemistry of disulfides and thiols to the practical task of shaping your hair (curling or straightening)? (A) Treat the hair with an oxidizing agent, shape them, and fix the new shape with a reducing agent. (B) Treat the hair with a reducing agent, shape them, and fix the new shape with an oxidizing agent. (C shape your hair, fix the new shape by the sequential treatment with an oxidizing agent, and then with a reducing agent. (D) None of these chemical techniques can work with actual hair because the peptide bonds in proteins are more important than the disulfide bonds. 65. Which of these alkenes will produce a more stable intermediate via a 12-hydride shift when it is reacted with HBr? (B) (C) 6. What is the product for this sequence of reactions? NaNH THF 2) H20 (A) HO OH NH (C) OH 67. Which of these functional groups is at the highest oxidation state? (B) aldehyde (A) alcohol D) carboxylic acid (C) alkane 68. Which is an intermediate for this O-O polymerization reaction? hv (B) (A) t-BuO t-BuO (C) t-BuO 69. Where would the stretching signal for the -OH of an alcohol group appear in the IR spectrum? (A) 1600 cm (B) 1715 cm (C) 1800 cm (D) 3300 cm'

Explanation / Answer

(64) (b)

(65) (a) It gives a tertiary carbocation

(66) (D)

(67) (d) Carboxylic acids (have two oxygens)

(68)(A) Peroxides produce free radicals and it is a tertiary free radical which is stable.

(69) (d) 3300 cm-1

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