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Question #45081

Difficulty: 8/10 | 🟢 Free

The Question

Consider the highly sterically hindered alkene, 2,2,5-trimethyl-3-phenyl-4-(2,4,6-trimethylphenyl)hex-3-ene. Isomer $\mathbf{A}$ of this compound is synthesized such that the phenyl group and the $-\text{CH}(\text{CH}_3)_2$ group are positioned on the same side of the $\ce{C=C}$ double bond axis (in terms of connectivity). Due to severe B-strain, the $\ce{C=C}$ bond is significantly twisted out of planarity.

Let $X$ be the formal Cahn-Ingold-Prelog (CIP) stereodescriptor value for Isomer $\mathbf{A}$ (Assign $X=1$ for $(E)$ , $X=2$ for $(Z)$ , and $X=0$ if the nomenclature is formally invalid due to the loss of planarity). Let $Y$ be the total number of formally $sp^2$ hybridized carbon atoms in the molecule. Let $Z$ be the number of planes of symmetry in its most stable twisted conformation at 298 K.

Calculate the value of $X + Y + Z$ .

Options

A.
14
B.
15
C.
16
D.
18

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

Cahn-Ingold-Prelog (CIP) Priority|Steric Hindrance (B-Strain)

Why This Question Is Tricky

Common Mistakes

This question tests three distinct traps.

First, the 'Chemical Exception' trap: students often assume that severe steric twisting (B-strain) invalidates E/Z nomenclature because the molecule is no longer planar ( $X=0$ ).

However, IUPAC CIP rules are topological, so the descriptor remains formally valid.

Second, a common CIP trap: confusing steric bulk with atomic number priority.

Students might incorrectly assign tert-butyl a higher priority than phenyl due to its size, leading to a false $(Z)$ assignment ( $X=2$ ).

Third, it tests the ability to identify $sp^2$ centers and 3D symmetry in sterically hindered, non-planar systems.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Cahn-Ingold-Prelog (CIP) Priority
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free