OChem Class 1

Question 1

Saturated Alkanes

Answer 1

All carbons have maximum number of H atoms attached

CnH2n+2

Question 2

Degree of Unsaturation

Answer 2

H2 molecule is removed

DOU = (2n+2) - x /2

x = # of hydrogen atoms
n = # of carbon atoms

Halogen acts like hydrogen atoms
O2 does nothing
Nitrogen has to be subtracted from the total of hydrogen atoms

Question 3

Properties of Unstable vs Stable molecule

Answer 3

Unstable:

• high reactivity with environment
• shorter lifespan
• high in energy

Stable:

• Low reactivity with environment
• longer lifespan
• low in energy

Question 4

Ring strain & strain energy

Answer 4

Ideal sp3 bond angle is 109.5, if it differs from this, it’ll cause ring strain

3 membered ring has more strain than 4
5 membered ring has minimal
6 =0
7 + = acts similar to 5 membered ring
14 = 0

Question 5

What does ring strain do?

Answer 5

Destabilizes ring, weakens C-C bond, increases reactivity

Question 6

What molecule can relieve ring strain?

Answer 6

H2 as a catalyst (usually in alkenes & alkyenes, not alkanes)

Question 7

Electropositive vs Electronegative substituents

Answer 7

Electropositive - Donate e- density (eg. alkyl groups)

Electronegative - Withdraw e- density (eg. O, halogens)

Question 8

Induction

Answer 8

Electrons in a sigma bond shift toward the more electronegative atom
FONClBrSCH

Question 9

Carbocation stability

Answer 9

tertiary > secondary > primary > methyl

Question 10

Carboanion stability

Answer 10

tertiary < secondary < primary < methyl

Question 11

Resonance stabilization

Answer 11

Occurs due to delocalization of electrons

Electrons travel from nucleophillic (high negative charge) to electrophillic (low negative charge)

Question 12

Resonance rules

Answer 12

1. Octet satisfied for ALL atoms
2. Least formal charge
3. Negative charge on the more electronegative atom

Question 13

Bronsted-Lowry Acid

Answer 13

Donates H+ and leaves behind conjugate base

The more stable conjugate base is, the strong the acid

Question 14

3 factors that influence conjugate base stability

Answer 14

1. Electronegativity- A more EN atom attached to H can handle negative charge better
2. Resonance - Increases stability of anionic conjugate base
3. Induction - proximity & electronegativity of EWG

Question 15

Strong acids to weak acids list

Answer 15

HBr, HI, HCl, HNO3, H2SO4, HClO4 > Sulfonic acid > carboxylic acid > phenol > alcohol & water > ketone & aldehyde > sp hybrid > sp2 hybrid > sp3 hybrid

Question 16

Nucleophile vs Electrophile

Answer 16

Electrophile is electron loving, accepts e- pair

Nucleophile is nucleus loving, donates e- pair

Question 17

Lewis base vs acid

Answer 17

Lewis base donates e-

Lewis acid accepts e-

Question 18

Nucleophilicity trend

Answer 18

Increases right to left, top to bottom

Question 19

Leaving Groups

Answer 19

• Parallel acidity (good leaving group = good acid)

- A good LG means it is a weak base of a strong acid, resonance stabilized or neutral LG. (water)

Question 20

What makes a molecule more stable?

Answer 20

Resonance
Induction
Size
Electronegativity

Question 21

What does reactivity depend on?

Answer 21

Leaving group ability
Nucleophile strength
Acid strength

Question 22

Isomer

Answer 22

Same molecular formula with different compounds

Question 23

Constitutional vs Conformational Isomer

Answer 23

Constitutional (structural)
- different atomic connectivity thus different chemical & physical properties

Conformational
- same atomic connectivity & identical chemical & physical properties

Question 24

Newman projections for n-butane

Answer 24

If methyl groups are 180° apart it is ANTI, and if H groups are 60° apart it is staggered (most stable)

If methyl groups are 60° apart it’s GAUCHE (intermediate stable)

If methyl groups are 0° apart (eclipsed) it is SYN (least stable)

Question 25

When drawing chair conformations

Answer 25

- Axial alternates up and down - Equitorial alternates opposite to that - When you have large substituent, better to be equitorial than axial because of unfavourable steric interactions

Question 26

Trans vs cis

Answer 26

Trans - both groups facing opposite direction | Cis - both groups facing same direction

Question 27

Chirality

Answer 27

Not superimposable on its mirror image | No plane of symmetry

Question 28

How to locate a chiral center

Answer 28

1. sp3 hybridization 2. tetrahedral geometry 3. 4 different substituents * carbons part of pi bond (double bond) won't have chiral center because it'll only have 3 groups NOT 4

Question 29

How to calculate number of isomers knowing how many chiral centers

Answer 29

2^n | n = # of chiral centers

Question 30

Optical Acitivty

Answer 30

Chiral molecules rotate plane-polarized light & are optically active d = dextrorotary (clockwise) + l = levorotary (counterclockwise) - +/- --> optical rotation d/l --> relative sterochemistry

Question 31

Assigning priority to atoms bonded to chiral center

Answer 31

1. Atom with highest atomic number has highest priority 2. Heavier isotopes have higher priority 3. if two atoms on a chiral center are identical, move to the next atom to find the first point of difference; the atom with the highest atomic number takes priority 4. Bonded atoms count as an equivalent number of single bonded atoms

Question 32

Absolute configuration (R & S)

Answer 32

1. Assign priority (1-4) to atoms directly bonded to chiral center 2. Ensure lowest priorty substituent is in the "away" (dashed) position. If not, switch it with the substituent that is taking that place 3. Trace arc going from 1-3 - Counter-clockwise = S - Clockwise = R * If an exchange happened in step 2, use the reverse letter

Question 33

Steroisomers

Answer 33

Same connectivity but differ in spatial arrangement | Can be diasteromer, enantiomer or meso compound

Question 34

Enantiomer

Answer 34

- Non superimposable, mirror images - Opposite configuration at ALL chiral centers - Each enantiomer has optical rotation of equal magnitude, but opposite sign - All other chemical & physical properties are identical - Process to separate enantiomers is resolution

Question 35

Meso Compounds

Answer 35

- Must contain chiral centers - Have internal plane of symmetry - not optically active (achiral)

Question 36

Diastereomer

Answer 36

- Non-superimposable, non mirror image - All chemical & physical properties are different - Unrelated optical activities - Opposite configuration for at least ONE but not all chiral centers Can be either Geometric isomer OR Epimer

Question 37

Geometric Isomer

Answer 37

Does not need chiral center Restricted rotation about double bond or ring All chemical/physical properties are different Z/E ---> Cis/trans Trans is better because less steric interaction

Question 38

Epimers

Answer 38

Differ at ONLY ONE chiral center