CHEM 222 Chap 4 Alkanes HW F21 KEY cor PDF

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Homework answer key. You should study this....

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CHEM 222 Homework for Chapter 4, Alkanes 1. Draw and name all the structural isomers of heptane as indicated below WITHOUT USING ANY BOOKS OR THE INTERNET. (Wikipedia will have the answers, and you’ll learn nothing by looking them up.) Ignore chirality, which we haven't done yet. a) Draw all of them as line structures, as those are the easiest to compare quickly. There are nine you should come up with, ignoring enantiomers. b) Name all of them with each name next to its structure. c) Pick one structure, give its molecular formula, and draw it as both a condensed structure (all atoms specified, but no C-H bonds shown) and as a fully expanded structure (all C-H bonds shown), but without stereochemistry.

3,3-dimethylpentane 2,2,3-trimethylbutane

heptane

2-methylhexane

3-methylhexane

2,4-dimethylpentane

3-ethylpentane

2,3-dimethylpentane H

C7H16

H3C

CH3

CH2

H H

C

CH2

H3C

CH3

2,2-dimethylpentane

H

H

C

C H

H

H H

C C

C H

H

C H

H C

H

H

H

2. The following compound has a 12 carbon chain as its longest carbon chain (check to be sure yourself), which means it is a substituted dodecane.

tert-butyl

isobutyl

sec -butyl

isopropyl

a) Label each substituent as isopropyl, isobutyl, sec-butyl, or tert-butyl. b) Now name this substituted dodecane. 5-(sec -butyl)-4-( tert-butyl)-6-isobutyl-9-isopropyldodecane

4-(tert-butyl)-5-(sec-butyl)-6-isobutyl-9-isopropyldodecane would be acceptable, but "sec" and "tert" are alphabetized as the tie-breaker, not the numbers.

3. Draw the structure and indicate what is wrong with the following names, then give a corrected name. There may be more than one correct answer. a) sec -pentyl chloride This name is ambiguous and is never used because of that. Cl or Cl 3-chloropentane

2-chloropentane

b) 2-chloro-4,5-dimethylhexane Numbered wrong-the substituent on the second carbon from either end is a tie, so the second methyl group determines the direction of counting. [Note this gives the smallest numbers overall, but that is not the rule here. See the counter example on the right.]

2,3,8,8,9,9,11-heptamethyldodecane NOT 2,4,4,5,5,10,11-heptamethyldodecane Compare:

Cl 5-chloro-2,3-dimethylhexane

c) 1,4,5-trimethylcyclohexane Mis-numbered again-started at the wrong carbon AND went the wrong way around the ring.

1,2,4-trimethylcyclohexane

OH

OH

H

X

H

H H O

H H

H

H

H HO

O

HO Testosterone

Estradiol

HO O

H H

H

H

H

OH

H H

HO

H

H OH

OH

O

X

OH OH

H

H

H

O

H

H

X

H

H

H

HO

OH H HO

4. Larry Laisie is not very careful with his structures. He did practice copying the structures of testosterone and estradiol, the major male and female hormones, but he was in too much of a hurry to proofread his structures. Use the two correct structures with the names to find and correct his mistakes in the other seven structures.

5. Give the cyclohexane shown an IUPAC name, but using isopropyl etc. (IUPAC accepts these common "radical" names as alternatives to the most official names.) Number the cyclohexane ring as shown.

Cl 2 1

2-(sec -butyl)-1-( tert-butyl)-4-chloro-5-isobutyl-3-isopropyl-6-propylcyclohexane

6. Draw 2-chloro-5-methylbicyclo[2.2.2]octane.

or Cl

etc. Cl

7. Draw an energy diagram for the rotamers of 2,3-dimethylbutane using Neuman Projections. Show the relative energy of the maxima and minima, and assign numbers to the energy levels based on the numbers in the slide.

30 kJ/mol

24 kJ/mol

11 kJ/mol 8 kJ/mol

8. Draw cis-1-chloro-4-ethylcyclohexane in both chair forms. Which chair conformation is more stable and why?

CH3 H

Cl H

H

H

Cl

CH2

Cl

H

H

H

H H

H

H

CH3 CH2

H H

H HH

H

H

HH

The chair on the right would be lower in energy (more stable). Methyl and chloro are about the same size, but the C-Cl bond is longer, as Cl is a third period atom. This puts it further away from the two axial hydrogens it has 1,3-interactions with....