Chapter 1: Bonding And Stereochemistry

Question 1

Nucleophile vs electrophile

Answer 1

1. Nucleophile: atom or functional group that forms a bond by donating a pair of electrons from a lone pair or pi bond (Lewis base)
   1a. Means nucleus loving…therefore any negative charge (electrons)
   1b. Attack Electrophiles (arrow is from nucleophile to electrophile)
2. Electrophile: the atom or functional group with the concentration of positive charge

Question 2

Index of hydrogen deficiency (IHD) / degree of unsaturation (DoU)

Answer 2

1. IHD=((2n+2)-H-X+N) /2
   1a. N=number of carbons
   1b. H=number of hydrogens
   1c. X=halogens (only if heteroatoms)
   1d. N=nitrogen (only if heteroatoms)
2. Oxygens don’t change the IHD

Question 3

Nomenclature functional groups

Answer 3

1. Carboxylic acid: RCOOH: -oic acid
2. Anhydride:
3. Ester: RCOOR’ : -oate
4. Amide: H2NCOR
5. Aldehyde: RCOH
6. Ketones: RCOR’
7. Alcohols: ROH
8. Thiol: R-SH
9. Amines : R-NH2
10. Alkene, alkyne, alkane

Question 4

Carbon numbers

Answer 4

1. Meth
2. Eth
3. Prop
4. But
5. Pent
6. Hex
7. Hept
8. Oct
9. Non

Question 5

Max number of Stereoisomers on a molecule

Answer 5

=2^n where n=number of chiral centres

Question 6

Types of bonds

Answer 6

1. Types:
   1a. Sigma: formed by head on overlap of orbitals along the axis between atoms
   1b. Pi: formed by side on overlap of parallel p orbitals
2. Every bond has 1 sigma bond, the higher the bond order=more pi bonds
   2a. High bond order=high bond strength=high energy required to break bond=high stable=low potential energy=smaller bond length

Question 7

Lewis structure

Answer 7

1. Carbon atoms are usually central
2. Central is usually least EN
3. Halogens (F, CL, Br, I) are usually terminal
4. Hydrogen is always terminal

Question 8

Exceptions to the octet rule

Answer 8

1. Incomplete valence (ex: boron and its group)
2. Expanded valence (ex: S, P, Cl-)
3. Odd electron

Question 9

Formal charge

Answer 9

1. FC=VE-Dots-sticks

Question 10

Lewis structure of oxyacids (hydrogen-nonmetal-lots of oxygens)

Answer 10

1, hydrogen is bonded to the oxygen

Question 11

Major resonance structures have:

Answer 11

1. Full octet
2. Minimum number of formal charges
3. Negative formal charge on electronegative atoms
4. Minimum separation between opposite formal charges

Question 12

What are the notations of molecular structures that appear on the MCAT

Answer 12

1. Line diagram: just draw line to represent carbons
2. Wedge dash diagram: wedge is coming to you, dash is going away from you
3. Fisher projection: horizontal/wedge to you, vertical/dash away from you

Question 13

VSEPR Theory: basic geometry

Answer 13

1. Hybridization: basic geometry : angles
   1a. Sp: linear: 180
   1b. Sp2: trigonal planar : 120
   1c. Sp3: tetrahedral: 109.5
   1d. Sp3d: trigonal bypyramidal: 90, 120
   1e. Sp3d2: octahedral: 90
2. When doing this: lone pair is one group, double bond is one group (sp2), triple bond is one group (sp) etc.
3. When an atom has resonance: it will choose the planar configuration (ex: sp2 vs sp3…will choose sp2)

Question 14

VESPR Theory: molecular geometry

Answer 14

1. Types
   1a. Bent: AX2E
   1b. Trigonal bypyramidal: AX3E
   1c. Bent: AX2E2
2. The more electrons, the smaller the angles

Question 15

Delocalized electrons

Answer 15

1. Electrons that extend over multiple bonds or atoms: movement of electrons from responance structures
2. Increases stability of aromatic compounds

Question 16

Is a structure aromatic?

Answer 16

1. Planar/fully conjugated: sp2
2. Cyclical
3. Obeys huckels rule: 4n+2=pi electrons (n=0, 1, 2, 3)
   3a. 1 double bond=2 electrons
   3b. Only count lone pairs of electrons when an atom is not attached to a double bond!

Question 17

Chirality

Answer 17

1. Chiral molecules don’t have a plane of symmetry: so they rotate plane polarized light
2. Chiral/sterogenic carbons: attached to 4 different groups

Question 18

Isomers

Answer 18

1. Conformational (Conformers) isomers: same molecular formula and connectivity but structure differs by rotation around carbon-carbon single bonds (shown in Newman projections)
   1a. Eclipsed: high energy=least stable=big groups overlap=steric hinderance
   1b. Staggered: low energy=more stable=big groups opposites (anti staggered; most stable) or big groups far apart (gauche staggered)
2. Constitutional (structural) isomers: different atom connectivity (move around skeleton)
3. Stereoisomers: same atomic connectivity but different arrangement in space
   2a. Enantiomers: opposite stereochem at all stereo centres, identical physical properties (only difference is they react different in chiral environment & rotate plane polarized light in opposite directions)
   2b. Diastereomers: must have at least 1 diff and 1 same stereocentre (ex: cis/trans or E/Z alkanes)
   2bi. Epimers: differ at only one chiral carbon
   2bi1. Anomers: type of epimer that is a cyclic carb that differs at only one chiral carbon (Alpha: when C1 and C6=opposites (alpha=down), Beta: when C1 and C6=same (alpha is up))

Question 19

Geometric isomers: (cis/trans , E/Z)

Answer 19

1. Cis/trans
   1a. Cis: 2 long carbon chains on same side
   1b. Trans: 2 long carbon sides are on opposite sides (more stable)
2. Cahn ingold prelog state
   2a. Z: 2 high priority on “zee” same side
   2b. E: enemies: on opposite sides

Question 20

Absolute configuration: R (right) vs S (left)

Answer 20

1. Rule 1: if lowest priority is at back… number others in order of priority and count
2. Rule 2: if lowest priority is at front… number others in order of priority, count, and switch to opposite sign
3. Rule 3: if lowest priority is not at front or back…
   3a. Switch group to get it in back, and switch other two groups…count as rule 1

Question 21

Racemic mixture

Answer 21

1. A mixture that is 50:50 of 2 enantiomers so there is no net rotation of plane polarized light
   1a. Can be separated if enantiomers react with another chiral molecule to produce Diastereomers salts

Question 22

Meso compounds

Answer 22

1. Compounds that have a chiral carbon, but are not chiral (they don’t have symmetry)
   1a. Need a min of 2 stereocenters,

Question 23

Types of chromatography

Answer 23

1. Thin layer: separate based on polarity
2. Gas: separate based on boiling points
3. Size exclusion: separates based on size
4. Ion affinity: separates based on charge
5. Affinity: separates based on affinity

Question 24

Resolution: Separation of enantiomers

Answer 24

1. Add enantiometrically pure reagent that forms salt w mixture
2. Reaction yields Diastereometric salts (non identical physical properties)
3. Now can physically separate the salts

Question 25

Liquid-liquid Extraction:

Answer 25

1. Organic solvent (non polar) has an aqueous solvent added (acidic, basic or neutral) and the phases separate …aqueous phase links bc denser

Question 26

Thin layer chromatography

Answer 26

1. Stationary phase: species stuck to plate ….Mobile phase: solvent that travels up plate 2. More polar compound is lower /stops earlier 3. Retention factors: distance compound travelled/distance solvent travelled