Propose a mechanism for the reaction of pent-1-yne with HBr in the presence of peroxides. Show why anti-Markovnikov orientation results.

Rearrangements can occur during the dehydration of 1° alcohols even though no 1° carbocation is formed—that is, a 1,2-shift occurs as the C − OH2+ bond is broken, forming a more stable 2° or 3° carbocation, as shown. Using this information, draw a stepwise mechanism that shows how CH3CH2CH2CH2OH is dehydrated with H2SO4 to form a mixture of CH3CH2CH = CH2 and the cis and trans isomers of CH3CH = CHCH3. We will see another example of this type of rearrangement in Section 18.5C.

Draw the SN1 and E1 products formed in the reaction of (CH3)3CBr with H2O.

The first step in the mechanism of reduction of an aldehyde or ketone with either LiAlH4 or NaBH4 is nucleophilic attack. Which of the following is the electrophilic site in this first step?

In the following reaction mechanism, what best describes the role of the Grignard reagent? + CH₂MgBr 1) ether 2) H3O+ The Grignard reagent acts as a nucleophile and attacks the carbonyl carbon. The Grignard reagent acts as an electrophile and is attacked by the oxygen. The Grignard reagent is first protonated by the acid. The Grignard reagent acts as a nucleophile and removes a proton from the methyl group attached to the carbonyl carbon.

Show how the reaction of an allylic halide with a Grignard reagent might be used to synthesize the following hydrocarbons.(a) 5-methylhex-1-ene

In addition to α cleavage, some aldehydes and ketones undergo theMcLafferty rearrangement. In the McLafferty rearrangement, a hydrogenon a carbon three atoms from the C=O is transferred to the carbonyl oxygen and a carbon–carbon bond is broken. This process forms an alkene and the radical cation derived from an enol, which appears as a fragment in the mass spectrum. Draw the products formed from the McLafferty rearrangement of 1-phenylpentan-1-one, and identify the fragment that results in the givenmass spectrum. If a mass spectrum of the ester ethyl pentanoate(CH3CH2CH2CH2CO2CH2CH3) is recorded, what is the mass of theradical cation formed by the McLafferty rearrangement?