Chapter 2: Isomers

Question 1

What causes ring strain?

Answer 1

Angle strain, torsional strain, non-bonded strain/steric strain

Question 2

What causes angle strain?

Answer 2

When bond angles are stretched or compressed from their normal size

Question 3

What causes torsional strain?

Answer 3

When cyclic molecules must assume conformations that have eclipsed or gauche interctions

Question 4

What causes non-bonded/steric strain?

Answer 4

When nonadjacent groups or atoms compete for the same space

Question 5

Define structural isomers & describe if they share physical/chemical properties

Answer 5

Isomers that share only a molecular formula and have different physical and chemical properties

Question 6

Define conformational isomers

Answer 6

Isomers that differ by rotation around a single bond

Question 7

Define staggered conformations of conformational isomers and the two subtypes

Answer 7

Have groups 60 degrees apart; subtypes are anti-staggered (180 degrees apart) and gauche staggered (60 degrees apart)

Question 8

Define eclipsed conformations of conformational isomers

Answer 8

Groups directly in front of each other as per Newman projections

Question 9

Which creates more non-bonded strain: axial or equatorial substituent positions

Answer 9

Axial

Question 10

In cyclohexane molecules with multiple substituents, the largest substituent will usually take up the ___________ position

Answer 10

Equatorial

Question 11

Define configurational isomers

Answer 11

Isomers that can only be interchanged by breaking and reforming bonds

Question 12

Define enantiomers and do they share physical/chemical properties

Answer 12

Enantiomers are non-superimposable mirror images (i.e., opposite stereochemistry at every chiral carbon); they share the same chemical and physical properties except for rotation of plane-polarized light and rxns in chiral environments

Question 13

Define optical activity

Answer 13

The ability of a molecule to rotate plane-polarized light

Question 14

D- molecules are also known as (__) and rotate light to the ______

Answer 14

(+); right

Question 15

L- molecules are also known as (__) and rotate light to the _______

Answer 15

(-); left

Question 16

Define racemic mixtures

Answer 16

Mixture with equal concentrations of two enantiomers; not optically active b/c enantiomers cancel each other out

Question 17

Define meso compounds

Answer 17

Compounds with chiral centres but an internal plane of symmetry that makes it optically inactive

Question 18

Define diastereomers and do they share chemical/physical properties

Answer 18

non mirror-image stereoisomers that differ at some but not all chiral centres. They have different chemical and physical properties

Question 19

Define cis-trans isomers

Answer 19

Subtype of diastereomers in which groups differ in position about an immovable bond (i.e., double bond or cycloalkane)

Question 20

Define relative configuration

Answer 20

Gives the stereochemistry of a compound in comparison to another molecule

Question 21

Define absolute configuration

Answer 21

Gives the stereochemistry of a compound without having to compare to other molecules

Question 22

An alkene is (Z) if the highest-priority substituents are on the ______ side of the double bond

Answer 22

Same

Question 23

An alkene is (E) if the highest-priority substituents are on the ______ side of the double bond

Answer 23

Opposite

Question 24

Switching one pair of substituents on a Fischer diagram…..

Answer 24

Inverts the stereochemistry of the chiral centre

Question 25

Switching one pair of substituents on a Fischer diagram….

Answer 25

Retains the stereochemistry of the chiral centre

Question 26

Rotating a Fischer diagram 90 degrees ….

Answer 26

Inverts the chiral centre

Question 27

Rotating a Fischer diagram 180 degrees…

Answer 27

Retains the stereochemistry