First midterm

Question 1

Define stereogenic center

Answer 1

A carbon atom (or other atom) in a molecule that is substituted in such a way that a new stereoisomer is produced when two substituents (on the same carbon/atom) are switched

Question 2

define chirality center

Answer 2

a carbon atom (or other atom) that is attached to four different substituents

Question 3

define conformer

Answer 3

Compounds that differ by orientation of atoms in space. They are interconvertible via
rotation about single bonds.

Question 4

define Constitutional isomers (also called structural isomers)

Answer 4

Compounds with the same chemical formula, but differ in their connectivity. They cannot be interconverted without breaking covalent bonds.

Question 5

define stereoisomers

Answer 5

Compounds with the same constitution (same numbering in name), but differ by the spatial arrangement of atoms. They cannot be interconverted without breaking covalent bonds.

Question 6

Define Enantiomers (optical isomers)

Answer 6

A pair of molecules that are mirror images of each other, but are not identical (no matter how they are rotated). Enantiomers are one type of stereoisomer.

Question 7

Define Chiral (handedness) compounds

Answer 7

Copounds that exhibit enantiomerism. Chiral compounds are optically active

Question 8

define achiral compounds

Answer 8

Compounds whose mirror images are superimposable. Achiral compounds are
optically inactive. Achiral compunds have a plane of symmetry

Question 9

Requirements for a compound to be chiral

Answer 9

(1) Has handedness
(2) can be separated into enantiomers
(3) is not superimposable on its mirror image.

Question 10

Define optical activity

Answer 10

Rotation of plane polarized light that occurs on passing through a sample containing one (or a majority of one) enantiomer. Rotation is measured using a polarimeter.

Question 11

Rotation of light in the right-hand direction (clockwise) is called _____

Answer 11

dextrorotatory, d, or (+)

Question 12

Rotation of light in the left-hand direction (counter-clockwise) is called ______

Answer 12

levorotatory, l, or (-).

Question 13

Define racemic mixture

Answer 13

a 1:1 mixture of corresponding enantiomers. Rotation = 0° because enantiomers have equal but opposite optical activity.

Question 14

define optically pure

Answer 14

One and only one enantiomer is present.

Question 15

define optically active

Answer 15

a majority of one enantiomer is present.

Question 16

define optically inactive

Answer 16

a majority of one enantiomer is present.

Question 17

define diastereomers

Answer 17

Stereoisomers that are not enantiomers. Diastereomers have different properties.

Question 18

define meso compound

Answer 18

Compounds that have more than one stereogenic center, but are achiral (and have stereoisomers that are chiral).