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Question #44468
The Question
Consider the stoichiometric halogenation of (Z)-2-butene using the neutral octahedral complex (where bipy = 2,2'-bipyridine) in at 298 K. Due to the strong d-orbital contraction of the high-valent metal center, the electrophilicity of the coordinated chlorides is significantly enhanced. The reaction proceeds via alkene coordination followed by a locked, concerted cyclic transition state involving the transfer of two mutually \textit{cis} chloride ligands to the alkene. Identify the stereochemical nature of the major organic product and the final oxidation state of the transition metal.
Options
- A.
\textit{meso}-2,3-dichlorobutane ;
- B.
\textit{racemic}-2,3-dichlorobutane ;
- C.
\textit{meso}-2,3-dichlorobutane ;
- D.
\textit{racemic}-2,3-dichlorobutane ;
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Mechanism_Trap
Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.
Concepts Behind This Question
Stereochemical Outcome of Halogenation|Complex Ion Oxidation States|d-orbital contraction
Why This Question Is Tricky
Common Mistakes
The 'Chemical Exception' being tested is the stereochemical outcome of alkene halogenation.
Students are heavily conditioned by the heuristic that halogenation always proceeds via anti-addition (which would yield a racemic mixture for a cis-alkene).
The trap is failing to recognize that the transition-metal-mediated pathway, specifically an octahedral complex enforcing a locked cyclic transition state with cis-halides, overrides the radical/halonium pathway and mandates syn-addition.
Furthermore, it tests the student's ability to track complex ion oxidation states during a reductive elimination event, where the metal center must be reduced by two units (from +4 to +2) as the organic substrate is oxidized.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Hydrocarbons - Class 11 Part 2 |
| Concept | Stereochemical Outcome of Halogenation |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |