Name CHEM250 Esam I (17) October 12,2017 e nootionad ernergy diagram of butane i

Question

Name CHEM250 Esam I (17) October 12,2017 e nootionad ernergy diagram of butane is shown below. The indicated sawhoese structure of butanorrespond to the e the angle seale os the sop of the on the energy diagram? (Not cecrgy Sound pre) at which of the following roationl 16 kimol 3.8 kgimol A 180 B. 120 C. 6o D. 0 9. Which of these bases can depeotonaw acetyliene (ka 26)? The pKa values for the conjugate acids are shown in D. NaHCO, (63) L Boh B and C parentheses A. NaH (15.7 B. Butyllithium (50-60) C NNH, (36) 10. Which one of the following molecules woald have a chiral cester? ci c CI. H CI H C. Ca E. None of the above. None of the molecules shown is chiral 11. Identify the two atoms anti to the bromine in the structure shown A. the equatorial H's on C-2 and C Br C-2 and C-6 C the axial H's an C-2 and C-6 D. C-3 and C-5 E C-4 Page 2 of 7

Explanation / Answer

Analysis will be done on carbns --> C2-C3 respectively

C2 --> front carbon, bonded species --> to H, CH3, CH3

C3 --> back carbon, bonded species --> H, CH3, H

Note that

there are two main types of position; they are either:

- STAGGERED --> will have 60° separation between all groups, therefore, it is much more stable, the groups are the farthest away possible from all

- ECLIPSED --> Half of the Groups are 0° away from each other, the other half is at 120°.. This requires higher energy since it takes more energy to get together at the 0° configuration.

Also...

keep in mind that bulky groups... Bulky groups are those groups which are "larger" considered to other groups

The least bulky group/species is -H atom... since it is small.

Note that there are also energy considerations depending on the type of configuration:

Bulky - Bulky --> most energy

Bulky - nonbulky --> medium energy requirement

nonbulky - nonbulky --> least energy

note that

CH3-CH3 is Eclipsed, therefore

requires energy

and CH3-CH3 is the most bulky interaction, therefore

it must be 19 kJ/mol, i.e. 0°

Q9

deprotonate --> will react as:

BH+ + X --> B + HX

where BH+ is the protonated base

any species which is a better base will do

for instance --> butylithium and NaNH2

since NH2- + BH+ --> NH3 + B

choose E, B and C

Q10

chiral centers must have 4 different bonded atoms

A --> not chiral, since Cl repeats

b --> chiral, Cl, H, CH2CH2CH3, and CH3 are all different

c --> not chiral, since CH2CH3 repeats

d --> not chiral, since H and H repeats

choose only B

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