Multiple Choice
Which of the following differentiates PEP carboxylase from RuBisCO in terms of substrate specificity?
3. Acids and Bases
Organic Chemistry Reactions
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Which of the following statements about the reaction of alkenes with halogens is false?
A
Alkenes react with halogens in the presence of water to form halohydrins.
B
Alkenes react with halogens to form vicinal dihalides.
C
The reaction of alkenes with halogens involves a cyclic halonium ion intermediate.
D
Alkenes react with halogens to form alkynes.
Verified step by step guidance1
Begin by understanding the general reaction of alkenes with halogens. Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond, which is reactive towards halogens like chlorine (Cl₂) and bromine (Br₂).
Recognize that the typical reaction of alkenes with halogens results in the formation of vicinal dihalides. This occurs through the addition of halogen atoms across the double bond, resulting in a saturated compound.
Consider the mechanism of the reaction. The reaction often involves the formation of a cyclic halonium ion intermediate. This intermediate is formed when the halogen molecule approaches the alkene, leading to a temporary three-membered ring structure.
Understand the role of water in the reaction. When alkenes react with halogens in the presence of water, halohydrins are formed. Water acts as a nucleophile, opening the halonium ion and adding an OH group to one of the carbons.
Evaluate the false statement: 'Alkenes react with halogens to form alkynes.' This statement is incorrect because alkynes are formed by the removal of hydrogen atoms, not by the addition of halogens. The addition of halogens to alkenes does not result in the formation of alkynes.
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