Chapter 2 Isomers

Question 1

What is a constitutional isomer?

Answer 1

Same molecular formula different connectivity.

Question 2

What is a conformational isomer?

Answer 2

Temporarily different shape of the same atom.

Same molecular formula but differs by rotation about a single bond.

Question 3

What are the two types of configurational isomers?

Answer 3

Enantiomers and diastereoisomers

Question 4

What is a diastereoisomer?

Answer 4

A superimposable mirror image. Differs at one or more chiral center(s).

Question 5

What is an enantiomer?

Answer 5

A non-superimposable mirror image. All chiral centers are the exact opposite.

Example: our hands are enantiomers.

Question 6

Bond angle of anti-/staggered Newman projection

Answer 6

180

Question 7

Bond angle of gauche Newman projection

Answer 7

60

Question 8

Bond angle of an eclipsed Newman Projection

Answer 8

120

Question 9

Bond angle of a totally eclipsed Newman projection

Answer 9

0

Question 10

Which Newman projection has the highest and lowest energy’s?

Answer 10

The anti-confirmation has the lowest energy and is thus the most stable. The totally eclipsed confirmation has the highest energy and is thus the least stable.

Question 11

For the chair confirmation bulky groups prefer the axial or equatorial position?

Answer 11

Equatorial

Question 12

What happens during a chair flip?

Answer 12

All axial groups switch to equatorial position however whatever is up remains up whatever is down remains down.

Question 13

What direction do wedges and dashes point in all of this cyclo alkane confirmations? (Ex: boat)

Answer 13

Wedges up. Dashes down.

Question 14

What sign and direction is assigned to the dextrorotary atoms?

Answer 14

(D) + clockwise (right)

Question 15

What sign and direction is assigned to the levorotary atoms?

Answer 15

(l) left counter clockwise (-)

Question 16

What causes no optical activity?

Answer 16

When a mixture of positive and negative enantiomers are present in and make sure they cancel each other out.

Question 17

How do you calculate the total number of possible diastereoisomers?

Answer 17

2^n (where n is equal to the number of chiral centers)

Question 18

Are miso compounds chiral or achiral?

Answer 18

Achiral. They have a line of internal symmetry which makes them optically inactive.

Question 19

When are the E and Z forms used to characterize a molecule?

Answer 19

For polysaturated double bonds. When they contain large substituents.

Question 20

Fisher projections, do the horizontal lines represent wedges or dashes?

Answer 20

Wedges. They point out of the page.

Question 21

For Fischer projection items on the right side represent R or S confirmation?

Answer 21

S

Question 22

For Fischer projections items on the left to represent R or S confirmations?

Answer 22

R

Question 23

How can you retain the stereo chemistry and a Fischer projection?

Answer 23

180° switch or changing two pairs of substituents.

Question 24

How do you invert the stereo chemistry of a Fischer projection?

Answer 24

By doing a 90° switch or by switching only one pair of substituents.

Question 25

In order for something to be optically active what must be true?

Answer 25

It must not be superimposable on his mirror image

Question 26

Are chiral molecules optically active?

Answer 26

Yes

Question 27

Are achiral molecules optically active?

Answer 27

No

Question 28

What separation measures can be used to separate diastereomers?

Answer 28

Distillation and recrystallization

Question 29

What separation measures can be used to separate enantiomers?

Answer 29

Affinity chromatography