Chapter 4.7, Problem 18CC

7. Draw the two chair conformations for the molecule below. Given the corresponding energy values, place the conformations in the appropriate boxes. Substituent AG° (eq→ ax) (kcal/mol) -CN -CH, 0.2 NEC 1.7 less stable chair more stable chair Clearly explain why the energy barrier associated with a nitrile group (-CN) moving from an equatorial position to an axial position is much lower than for a methyl group (-CH3).

Sight along the C2-Cl bond of 2-methylpropane (isobutane). a. Draw a Newman projection of the most stable conformation. b. Draw a Newman projection of the least stable conformation. c. Make a graph of energy versus angle of rotation around the C2-Cl bond. d. Assign relative values to the maxima and minima in your graph, given that an H↔H eclipsing interaction costs 0 kJ/mol and an H↔CH3 eclipsing interaction costs 6.0  kJ/mol.

Draw the most stable structure of 2-methyl-5-propylcyclohexanol in the chair conformation. Use the cyclohexane conformation drawing tool and guide points to draw each structure. Click and drag to start drawing a structure. 0, X S 00 B ola Ar 图

Analyze the two Newman projections and determine the relationship between the two. How would you describe the relation between conformations when they are maintained at a temperature too low to permit them to interconvert? CH3 CH3 Br. H H H H A. Identify the relationship. They are identical. They are structural isomers. They are stereoisomers. They are conformers. H H -I H Br H B. What is the relationship at low temperatures? They are identical. They are conformational diastereomers. They are structural isomers. They are conformational enantiomers.

10. Identify the higher energy and lower energy forms of two substituted cyclohexanes, for example t-butyl cyclohexane. Which form (t-butyl axial or equatorial) has a higher energy, and why? more stable by 24 kJ/mol H3C,CH3 CH3 C CH3 CH3 HaC-C Ke >1 H. H tert-butyl group axial tert-butyl group equatorial

For rotation about the C-a – C-b bond, using the following templates, draw the Newman Projection of the two staggered conformers that are different in energy. Fill each bond on Newman Projection with Hydrogen or Substituents. You may use Abbreviations such as Me for Methyl, Et for Ethyl, iPr for isopropyl. Circle the Newman projection of the most stable conformer.

Given cyclohexane in a chair conformation, construct the more stable conformation of cis-1-ethyl-2-fluorocyclohexane by filling in the missing atoms or groups. Use the numbering provided on the ring. H. Answer Bank H 5 1 H. F H ethyl 3 H

4 Practice 2 3-9 4.8 Conformational Analysis of Butane The graph below represents the relative energies of the conformations of butane: ww B Relative energy -1- —— 0° 60° 120° 180° 240° 300° 360° Angle of rotation Select the Newman projection that corresponds with position C on the graph (an angle of rotation of 120 degrees). HA 3 H I I I I # CH3 CH 3 CH 3 CH3 -I H HH CH3 CH3 CH3 80⁰0 CH3 H I I Н 4 000 000 % 6 MacBook Air 7 8 DIL FB 9 0

Using the wedge-and-dash notation, draw the nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane. A. From the nine stereoisomers, identify one pair of enantiomers. B. Draw the most stable conformer of the most stable stereoisomer.