Stereochemistry

Question 1

Who discovered ppl?

Answer 1

1800’s Louis Posteur

Question 2

What do molecules do?

Answer 2

Molecules rotate the plane of polarized light

Question 3

Equation for optical activity?

Answer 3

α
[α] = ————-
ℓ x C

[α] = optical activity specific rotation
α = observation rotation
ℓ = path/length 1dm
C = g/mL

Question 4

Chiral?

Answer 4

Handedness. Mirror image is non-superimposable. Rotates the plane of polarized light

Question 5

Chiral carbon?

Answer 5

Has 4 different sides (environments)

Question 6

Recemic Mixture?

Answer 6

1:1 mixture of enantiomers

Question 7

Mesomers?

Answer 7

Mirror image, chiral center, internal plane of reflection. They are the same except one is R one is S. R reflects as S through a mirror plane

Question 8

Optical rotation?

Answer 8

Rotation of plane of polarized light. Can have (+) or (-) rotations
Enantiomers (+-) or (d/ ℓ) or (D/L)

Question 9

Who made fisher diagrams?

Answer 9

Emil Fisher

Question 10

What are the rules for D/L?

Answer 10

1) Put enantiomer in a fisher with, highest oxidized carbon at the top.
(R-COO-H 3/4 bond to O) (CH3 not oxidized)

2) Put the lowest oxidized carbon (usually methyl) at bottom of fisher
3) Start at the bottom and look up until there is a atom with unpaired electrons
4) If atom with unpaired electrons is on the right is D, if on the left it’s L

Question 11

What is the flaw with D and L?

Answer 11

Doesn’t take in to account the rest of the chiral centres. Cannot distinguish between enantiomers

Question 12

Can you flip a fisher?

Answer 12

You cannot flip molecule because the horizontal arms will be going backwards instead of giving a hug

Question 13

What do R and S mean?

Answer 13

R—> Rectus (clockwise +)
S—> Sinister (counter clockwise -)

Label chiral centre 1 to 4 in order from highest to lowest atomic number

Question 14

Can R and S change?

Answer 14

The cannot change unless bonds are broken.

Question 15

Is there a trick to R and S?

Answer 15

Yes! If the H is in your face. To the right of a fisher or the top of a staggered. Don’t flip the molecule do the opposite of what you originally got. S will be R and R will be S

Question 16

Diostereomers?

Answer 16

Change of one chiral centre. Not the same. One is R one is S

Question 17

Can you make any molecule a diostereomer?

Answer 17

Yes you can change any amount of R’s to S as long as it is not all of the chiral centres. You can change one, two, three, four, five

Question 18

Wedged vs hashed

Answer 18

Wedged is coming out of page. If it is H it is coming out of page so switch R to S or S to R. Hashed is going behind

Question 19

What do you do when converting Newman projection to fisher.

Answer 19

Flip the one side 180 degrees

Question 20

What is 2^n

Answer 20

Indicated the total amount of stereoisomers. N is the amount of chiral centres in a molecule. If a mesomer is possible subtract 1

Question 21

Optical activity?

Answer 21

Rotation the day of polarized light

Question 22

When solving for the specific rotation what do you do?

Answer 22

Look at the ratio. Add together the whole ratio then use the final number as a fraction 1/x.

One enant has +10 the other must have -10. The ratio is 1:1

1/2(10) + 1/2(-10) = [α]

Question 23

What is %ee?

Answer 23

Percent enantiomeric excess

Question 24

How to solve for %ee?

Answer 24

Add together the whole ratio. Subtract each ratio number by the total. Subtract the bigger ratio number by the smaller. Put the express ratio number over the total for the %ee

3:1 —> 4
3-1 —>2 2/4 —> %50

Question 25

Alkane?

Answer 25

Comes from crude oil. Aliphatic chemistry (greasy). Sp3, Sp2 must be all hydrocarbons (CH). The longer the chain the greasier the molecule.

Question 26

What is catalytic cracking?

Answer 26

Breaks down long molecules of hydrocarbons into little pieces

Question 27

Who discovered ring sizes?

Answer 27

Von Baeyer and Saches in the early 1800

Question 28

What ring size is the most stable and least stable?

Answer 28

Most stable. 6 carbon ring. It is predominate in nature. Least stable is the three carbon ring. There is ring strain, it is unstable and very reactive

Question 29

What happens when rings pucker?

Answer 29

It forms a chair conformation. Forms from a 6 sided compound

Question 30

Where are axial bonds?

Answer 30

The point upwards from the ring

Question 31

Where are equatorial bonds?

Answer 31

They always point away from the ring. Count two bonds away from the axial bond to find the angle of the equatorial bonds.

Question 32

What is more stable for larger molecules? Axial or equatorial?

Answer 32

Always put larger groups on equatorial bonds because of on an axial the molecules butt heads. Further, the bigger the molecule the lower the energy!

Question 33

How does chair flipping work?

Answer 33

Makes every down peak up and up peak down. Changes every axial to equatorial and every equatorial to axial.

Question 34

How do you lock a chair from flipping?

Answer 34

Add a big group onto the equatorial bond.

Question 35

What is 1/2 a chair flip?

Answer 35

A boat conformation. They are more unstable.

Question 36

How do you add substituents to a chair diagram?

Answer 36

Start with a blank chair conformation and number the carbons in your cyclohexane and your chair. Make sure your number the same direction for both molecules (clockwise or counterclockwise). Add the atoms to the chair. If wedged. Add it to the up position, of dashed add it to the down position.

Question 37

What is the cahn- ingold- prelog system?

Answer 37

The absolute configurations. R and S

Question 38

How do you rank the atoms for R and S?

Answer 38

By atomic number

Question 39

Constitutional isomer?

Answer 39

Compounds with the same molecular formula but different structural formulas

Question 40

Stereoisomers?

Answer 40

Isomers with the same composition but different orientations

Question 41

Achiral?

Answer 41

A molecule that is superimposeable with its mirror image

Question 42

What is a stereogenic centre?

Answer 42

A chiral centre