Exam 2

Question 1

What type of halide is this?

Answer 1

Vinyl Halide

halogen directly attached to a double bonded carbon (C=C)

Question 2

What type of halide is this?

Answer 2

Allyl Halide

halogen bonded to the adjacent carbon in a double bond

Question 3

What type of halide is this?

Answer 3

Aryl Halide

halogen attached to a benzene ring

Question 4

What type of halide is this?

Answer 4

Benzylic Halide

halogen bonded to a carbon adjjacent to a benzene ring

Question 5

What does “sec” refer to in nomenclature?

Answer 5

The functional group is placed on a 2° Carbon

Question 6

What is the difference between a nucleophile and a base?

Answer 6

Nucleophiles attack e^- deficient atoms.

Bases attack protons (H⁺).

Question 7

What 3 factors help determine the strength of a nucleophile?

Answer 7

1. Stronger base = stronger Nu^-
2. Negatively charged Nu^- = stronger Nu^-
3. The farther left on the table = stronger Nu^-

Question 8

What is the general procedure for an S_N2 Reaction?

Answer 8

Replace leaving gropu w/ nucleophile.

Invert stereochemistry at stereogenic center

(in cyclo, simply change wedge/dash)

Question 9

Which mechanism (S_N1 or S_N2) is one step, concerted?

Answer 9

S_N2

Question 10

How do you draw the S_N2 Transition State molecule?

Answer 10

Draw the original leaving group molecule w/ dotted lines to the leaving group and nucleophile.

Question 11

Which mechanism (S_N1 or S_N2) does racemization always occur?

Answer 11

S_N1

Question 12

What is racemization?

Answer 12

Where both enantiomers are made (R & S).

Question 13

Which mechanism (S_N1 or S_N2) is 2-steps?

Answer 13

S_N1

Question 14

How many steps are in each of the following reactions?

S_N1

S_N2

Answer 14

S_N1: two steps

S_N2: one step

Question 15

How do you determine whether or not a reaction will be S_N1 or S_N2? (3x)

Answer 15

1. Classify the halide as 1°, 2°, 3°.
2. Classify the halid as strong/weak.
3. Classify the solvent as polar protic or polar aprotic.

Question 16

Which mechanism is favored by 1°?

Answer 16

S_N2

Question 17

Which mechanism is favored by 2°?

Answer 17

either (need more info)

Question 18

Which mechanism is favored by 3°?

Answer 18

S_N1

Question 19

Strong nucleophiles favor which mechanism?

Answer 19

S_N2

Question 20

Weak nucleophiles favor which mechanism?

Answer 20

S_N1

Question 21

Polar protic solvents favor which reaction?

Answer 21

S_N1

Question 22

Polar aprotic solvents favor which reaction?

Answer 22

S_N2

Question 23

What type of solvents are these?

H₂O

Ethanol (CH₂CH₃OH)

Methanol (CH₃OH)

Ammonia (NH₃)

Acetic Acid (CH₃CO₂H)

Answer 23

Polar Protic

Question 24

What type of solvents are these?

Acetone (CH₃)₂CO

DMF

THF

Acetonitrile (C triple bond N)

DMSO

Answer 24

Polar Aprotic

Question 25

Which side are the arrows draw in S_N1 and S_N2 mechanisms?

Answer 25

Reactant side

Question 26

What is the rate for an S_N1 mechanism?

Answer 26

Rate = k [RX]

Question 27

What is the rate for an S_N2 mechanism?

Answer 27

Rate = k [RX][Nu^-]

Question 28

What makes for a better leaving group?

Answer 28

Weak bases (they're stable on their own) The weaker the base, the better the leaving group.

Question 29

What are 4, generally, bad leaving groups?

Answer 29

OH^- F^- NH₂ CH₃O^-

Question 30

What are the strong acids? (6x)

Answer 30

HI HCl H₂SO₄ HBr HNO₃ HClO₄

Question 31

What are some good leaving groups (4x)

Answer 31

Cl I Br HSO₄

Question 32

What happens to the rate of an S_N2 reaction if the solvent is switched from polar aprotic to polar protic?

Answer 32

Slow down reaction

Question 33

Draw the structure of THF

Answer 33

Question 34

What happens to the rate of an S_N2 reaction if the halid changes from tertiary to secondary to primary?

Answer 34

it gets faster 3 \> 2 \> 1

Question 35

% ee = ee = enantiomeric excess

Answer 35

% ee = % enantiomer B - % enantiomer A ## Footnote *or vice versa*

Question 36

What is a 50/50 ratio of enantiomers called?

Answer 36

Racemic mixture

Question 37

When it comes to chair conformations, up/up and down/down equals what? up/down and down/up equals?

Answer 37

cis trans

Question 38

Any time an S_N1 reaction is involved, consider "this" in addition to the carbocation.

Answer 38

Resonance (LP/pi bonds)

Question 39

When it comes to evaluating acidity, what are two of the most important factors?

Answer 39

1. Where the molecule falls on the pKa chart. 2. How easily the molecule/atom wants to give up an "H"

Question 40

Gauche

Answer 40

Angle greater than 0, but less than 120