The Newman projection has to be drawn and the reason has to be explained for the formation of more trans product. Concept introduction: Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes. Newman projections: The new conformations of compounds can be drawn and analyzed by Newman projections. A Newman projection visualizes different conformations of Carbon-carbon chemical bond from front to back with the front carbon represented as a black dot and the back represented as a circle. The angle between two hydrogens of a Newman projection is called as dihedral angle or torsional angle. This dihedral angle changes as the C-C bond rotates. Two conformations with special attentions are staggered and eclipsed conformation. Staggered conformation is the lowest in energy and the eclipsed conformation is the highest in energy. For example, Anti-conformation: The conformation with a dihedral angle of is called anti-conformation. The two methyl groups achieve maximum separation from each other. In other, methyl groups are closer to each other; their electron clouds are repelling each other, causing an increase in energy. This unfavorable interaction is called gauche interaction. E2 elimination: Alkyl halide forms an alkene from the abstraction of the proton from the β-carbon atom followed by elimination of the halogen in a single step.

Question

1-Chloro-1,2-diphenylethane can undergo E2 elimination to give either cis- or trans-1,2-diphenylethylene (stilbene). Draw Newman projections of the reactive conformations leading to both possible products, and suggest a rea- son why the trans alkene is the major product. 1) -CHCH2- "OCH3 -CH=CH- 1-Chloro-1,2-diphenylethane trans-1,2-Diphenylethylene 2) 1 Predict the major alkene product of the following E1 reaction: HOAC CH3CHCBr ? Heat ČH;CH3

Answer 1

Question

Chapter 11.SE, Problem 51AP

Interpretation Introduction

Interpretation:

The Newman projection has to be drawn and the reason has to be explained for the formation of more trans product.

Concept introduction:

Conformations: Rotation about C-C single bonds allows a compound to adopt a variety of possible three-dimensional shapes.

Newman projections: The new conformations of compounds can be drawn and analyzed by Newman projections. A Newman projection visualizes different conformations of Carbon-carbon chemical bond from front to back with the front carbon represented as a black dot and the back represented as a circle.

The angle between two hydrogens of a Newman projection is called as dihedral angle or torsional angle. This dihedral angle changes as the C-C bond rotates. Two conformations with special attentions are staggered and eclipsed conformation. Staggered conformation is the lowest in energy and the eclipsed conformation is the highest in energy.

For example,

Anti-conformation: The conformation with a dihedral angle of is called anti-conformation.

The two methyl groups achieve maximum separation from each other. In other, methyl groups are closer to each other; their electron clouds are repelling each other, causing an increase in energy. This unfavorable interaction is called gauche interaction.

E2 elimination:

Alkyl halide forms an alkene from the abstraction of the proton from the β-carbon atom followed by elimination of the halogen in a single step.

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1-Chloro-1,2-diphenylethane can undergo E2 elimination to give either cis- or trans-1,2-diphenylethylene (stilbene). Draw Newman projections of the reactive conformations leading to both possible products, and suggest a rea- son why the trans alkene is the major product. 1) -CHCH2- "OCH3 -CH=CH- 1-Chloro-1,2-diphenylethane trans-1,2-Diphenylethylene 2) 1 Predict the major alkene product of the following E1 reaction: HOAC CH3CHCBr ? Heat ČH;CH3

Name (including E/Z stereochemistry) the five alkenes that can produce 3-bromo-3-methylhexane on reaction with HBr. Draw the skeletal structure of each molecule.

(a) When cis-1-bromo-2-methylcyclohexane undergoes an E2 reaction, two products (cycloalkenes) are formed. What are these two cycloalkenes, and which would you expect to be the major product? Write conformational structures showing how each is formed. (b) When rans-1-bromo-2-methylcyclohexane reacts in an E2 reaction, only one cyclo- alkene is formed. What is this product? Write conformational structures showing why it is the only product.