Midterm CHM 255

Question 1

Lab 1 (Chirality and Liquid Crystals)

Describe a short procedure for lab 1

Answer 1

1. relfux unknown configuration + biphenyl carbonate
2. Dry refluxed dopant and crush with MBBA and EBBA
3. Observe on a slide when heated, cooled and sheared and through movie theater glasses (R and S)

Question 2

Lab 1

Liquid crystals

Answer 2

a state of matter between solid crystal and liquid with light reflecting properties, ‘Orderd fluids’

liquid: random structure, crystal: ordered structure

Question 3

Lab 1

Melting Point

Answer 3

Where a solid begins to melt, often cloudy

Question 4

Lab 1

Clearing point

Answer 4

Where a substance is completely liquid, no solid left, often clear

Question 5

Lab 1

Nematic Phase

Answer 5

phase before cholesteric, structure with all molecules fluid but point in the same direction, does not rotate light

Question 6

Lab 1

Cholesteric Phase

Answer 6

phase after nematic phase, helical structure that will reflect R or S light depending on what chiral molecule the nematic phase was treated with

Question 7

Lab 1

If you are heating a substance and it begins cloudy at 23 C and goes transparent at 32 C what is the melting and clearing points?

Answer 7

melting: 23 C
Clearing: 32 C

Question 8

Lab 1

Why do the liquid crystals turn clear when heated?

Answer 8

When heated the liquid crystal is no longer a crystal and is completely liquid, it loses its ability to rotate light so that is why it turns clear.

when cooled it returns to liquid crystal

Question 9

Lab 1

Why is no light reflected with a racemic mixture of liquid crystals?

Answer 9

Because the nematic phase is achiral, not helical and does not rotate light

Question 10

Lab 2 Reduction of m-dinitrobezene

Describe a short procedure for lab 2

Answer 10

1. reflux m-dinitrobenzne, copper, and hydrobromic acid for one hour
2. hot filter, cool filter again and add fitrate to ammonium hydroxide
3. extract filtrate using toluene
4. rotovap

Question 11

Lab 2

Oxidation

Answer 11

decrease in the number of electrons
- increases number of C-electronegative atom bonds
- decreases number of C-H bonds

Question 12

lab 2

reduction

Answer 12

increase in the number of electrons
- decrease in the number of C- electronegative atoms bonds
- increase in the number of C-H bonds

Question 13

lab 2

chemoselective

Answer 13

when a reagent will only react with one functional group on the molecule

Question 14

lab 2

stereoseletive

Answer 14

Both stereochemical products are made but one is favored over the other

ex: a Z alkene may be favored over an E alkene or vice versa

Question 15

lab 2

Stereospecific

Answer 15

Only one stereochemical product is made

Question 16

lab 2

Examples of Oxidizing reagents

I have 5 on this card

Answer 16

PCC, Chromic acid, potassium permangenate, Peroxy acids, O3

Question 17

lab 2

Examples of Reducing agents

i have three on this card

Answer 17

LiAlH, NaBH4 and H2 + metal catalyst

Question 18

Lab 3 (Diels Alder Reaction)

Give a short procedure for lab 3

Answer 18

1. relfux 9-anthraldehyde + anhydride + toluene for one hour
2. dry and vaccuum refluxed product
3. recrystallize with hexanes

Question 19

lab 3

Diene

Answer 19

conjugated with at least two alkene molecule that reacts with a dienophile in a diels alder reaction

must be in cis configuration to react

Question 20

lab 3

Dieneophile

Answer 20

diene loving molecule that reacts with the diene to form the adduct in the diels alder reaction

performs better w/ ewg

Question 21

lab 3

Why is the Diels Alder reaction a good examples of green chemistry?

Answer 21

bc it adheres to atom economy, the idea that waste should be limited
- in the reaction all reagents are incorporated into the products with no by products

Question 22

lab 3

In the product of a diels alder reaction what is preferred? Endo or Exo?

Answer 22

Endo is preferred so it can be closer to the double bond but also bc of kinetic control

Question 23

lab 3

The — the conjugation the higher energy is absorbed, aka the shorter the wavelength

Answer 23

less/lower conjugation

Question 24

lab 3

the more/higher the conjugation the — the energy absorbed and — the wavelength

Answer 24

the lower the energy and longer the wavelength

Question 25

lab 3

True or false? The stereochem of the dienophile is not conserved in the diels alder reaction

Answer 25

false, it is conserved

Question 26

lab 3

Is the forward diels alder reaction favored at high or low temperatures

Answer 26

the forward diels alder reaction is favored at low temperatures

Question 27

Lab 4

What does it mean for protons to be enantiotopic?

Answer 27

the protons are equivalent and by the z atom test they create one chiral center on the molecule

Question 28

Lab 4

What does it mean for protons to be homotopic?

Answer 28

they are equivalent and by the z atom test create no chiral centers

aka creates same molecule

Question 29

Lab 4

What does it mean for protons to be diastereotopic?

Answer 29

they are non equivalent and by the z atom test create 2 chiral centers or a 2nd chiral center on the molecule

Question 30

Lab 4

what does it mean for protons to be heterotopic?

Answer 30

They are non equivalent, and by the z atom test create constitutional isomers

Question 31

Lab 4

How do you calculate HDI?

Answer 31

of rings + # of pi bonds
or (C+1)+(N-H-x/2)

Question 32

Lab 4

What does the integreation number tell you?

Answer 32

the number of hydrogens contributing to that signal

Question 33

Lab 4

If your J values are similar what does that tell you about those protons?

Answer 33

they are likely close to each other on the molecule

Question 34

Lab 4

When looking at a H-H COSY what does the diagonal line tell you?

Answer 34

not much, it is basically a recreation of the 1D HNMR

look off the line for more info