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Chapter 11: Q28P (page 571)

Propose a mechanism for each reaction.

(a)

(b)

Short Answer

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(a)

(b)

Step by step solution

01

Pinacol rearrangement

Pinacol rearrangement transforms the 1, 2-diols into carbonyl compounds comprising a carbon-oxygen double bond. This happens through a 1,2-migration that happens under acyl conditions.

02

Products formed when the given starting material undergoes oxidation with the given reagents in reaction a

The given reactions form a category of the Pinacol-rearrangement. The first step is the protonation of a hydroxyl group. The next step is the loss of water to form a carbocation. The next step is the methyl migration forming a resonance-stabilized carbocation. The final step is the deprotonation leading to the product.

(a)The mechanism of the reaction can be given as:

Mechanism of reaction a

03

Products formed when the given starting material undergoes oxidation with the given reagents in reaction b

(b)The mechanism of reaction b can be given as:

Mechanism of reaction b

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Most popular questions from this chapter

Under normal circumstances, tertiary alcohols are not oxidized. However, when the tertiary alcohol is allylic, it can undergo a migration of the double bond (called an allylic shift) and subsequent oxidation of the alcohol. A particularly effective reagent for this reaction is Bobbitt’s reagent, similar to TEMPO used in many oxidations. (M. Shibuya et al., J. Org. Chem., 2008, 73, 4750.)

Show the expected product when each of these 3° allylic alcohols is oxidized by Bobbitt’s reagent.

(a)

(b)

(c)

(d)

Predict the products of the following reactions.

(a) cyclohexylmethanol + TsCl / pyridine (b) product of (a) + LiAlH4

(c) 1- methylcyclohexanol + H2SO4, heat (d) product of (c) + H2, Pt

Propose a mechanism for the reaction of

(a) 1-methyl cyclohexanol with HBr to form 1- bromo-1-methylcyclohexane.

(b) 2- cyclohexylethanol with HBr to form 1-bromo-2-cyclohexylethane.

Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent

(a) butan - 1 - ol → butanal, CH3CH2CH2CHO

(b) but - 2 - en - 1 - ol → but - 2 - enoic acid, CH3CH = CHCOOH

(c) butan - 2 - ol → butan - 2 - one, CH3COCH2CH3

(d) cyclopentanol → 1 - cyclopentylpropan - 1 - ol (twosteps)

(e) cyclopentyclohexanol → 2 - methylcyclohexanone (several steps)

(f) 1 - methylcyclohexanol → 2 - methylcyclohexanone (several steps)

Trichloroisocyanuric acid, TCICA, also known as “swimming pool chlorine,” is a stable solid that oxidizes alcohols, following a mechanism similar to oxidation by HOCl. No reaction occurs between TCICA and the alcohol (in a solvent such as acetonitrile) until one drop of HCl(aq) is added, whereupon the reaction is over in a few minutes. Write the mechanism for this oxidation that shows the key role of the acid catalyst. Show the oxidation of just one alcohol, not three. (Hint: The carbonyls are the most basic sites on TCICA.)
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