HYS CH2: Isomers

Question 1

isomers

Answer 1

same molecular formula

different types
1. consitutional isomers: share only molecular formular, different connectivity
- different reactivity, boiling points

2. steroisomers
   a. configurational isomers: Configurational isomers differ in the spatial arrangement of their atoms and can only be interconverted by breaking bonds (and not by free rotation about single bonds).
   - entantiomers (pairs differ in absolute configuration of all chiral center, mirror images)
   - diasteromers (

b. conformational isomers: 2 identical molecules with different orientations (Newman project down carbon center)

Question 2

which newman projection has minimal energy

Answer 2

staggered
low energy and stable

Question 3

which newman projection has high energy

Answer 3

eclipsed
high energy
steric hindrance

Question 4

enantiomers vs diasteromers

Answer 4

• entantiomers (pairs differ in absolute configuration of all chiral center, mirror images)
• diasteromers (pairs differ in absolte configuration at least 2 chiral center and therefore needs at least 2 chiral centers)

Question 5

epimers

Answer 5

a kind of diostereomer than differs in 1 chiral center and is a non mirror image

Question 6

which configurational isomers are optically active?

Answer 6

enantiomers that can rotate polarized light

Question 7

absolute configuration

Answer 7

to break a tie consider atoms attached to each of atoms
H are last priority

CCW –> S
CW –> R

• if the H is NOT going into the plane, then switch the assignment
• flipping it from S –> R

Question 8

glucose and galactose are what kind of isomers

Answer 8

diasteromers (epimers)
only one chiral center with differen OH/H configurations

Question 9

groups in the middle of fisher projection point

Answer 9

out of the page

Question 10

groups above and below chiral carbon point

Answer 10

into the page

Question 11

cis and trans

Answer 11

uses for alkenes (double) and alkanes (single)

oriention across a non rotatable bond

is if the two R groups are on the same side of the carbon-to-carbon double bond, and trans if the two R groups are on opposite sides of the carbon-to-carbon double bond.

Question 12

E/Z priority

Answer 12

used for alkenes

Z - zusammen
E - entgegen

based on high priority groups

Question 13

w

polarized light

Answer 13

molecules with chiral ceter

light through filter reflects only light in one direction

• and + show the shift in angle of light rotation
  + is clockwise
• is counterclockwise

+/- is experimental and not related to R/S
cant predict magnitude of rotation

Question 14

determine number of stereoisomers in a molecule

Answer 14

2^n
n is the number of chiral carbons in the molecule

carbons 2-5 are chiral– 4 carbons
2^4 = 16

Question 15

is axial and equatorial an example of what kind of isomer

Answer 15

conformational isomers
can rotate around a single bond and maintain same atomic connectivity

Question 16

what is true?

cis-2-butene
trans-2-butene
Z-2-butene
stability not related to configuration

Answer 16

increasing stability can be done by reducing steric hindrance (inc distance between substituents)

double bond of 2-butene means methyls can be on same side of double bond (cis) or opposite (trans)

trans increase seperation of methyl groups conferring greater stability and reducing steric hindrance

in Z they are on same side and are cis