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MCAT Organic Chemistry > O Chem > Flashcards

O Chem Flashcards

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1
Q

Molecular Bonds

A

Longer bonds are weaker bonds
Triple > Double > Single
Sigma bonds > Pi bonds

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2
Q

sp3 Hybrid Orbitals

A

s+p+p+p
109.5 degree angle
Tetrahedral, Bent (2 lone pairs), Triganal Plane (one lone pair)
4 sigma bonds

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3
Q

sp2 Hybrid Orbitals

A

s+p+p
120 degree angle
Triganal planar

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4
Q

sp Hybrid Orbitals

A

s+p
180 degree angle
Linear

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5
Q

Acid Strength by Orbital

A

The more s character in a hybrid orbital, the stronger the acid
sp > sp2 > sp3

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6
Q

Resonance

A

e- density is shifted through regions of a molecule via pi bonds
Resonance reduces basicity (makes an atom more acidic)
Rules:
1) Atoms should have filled orbitals
2) Best structure minimizes formal charges
3) (-) charge is best placed on most electronegative atom
4) (+) charge is best placed on least electronegative atom

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7
Q

Inductive Effect

A

Induces charge separation in a molecule b/c of delocalization of e- by electronegative atom

  • Transfer of e- through sigma bond
  • Dissipates over distance
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8
Q

Steric Hindrance

A

Occurs when two atoms attempt to be in same place at same time
Large substituents should be equitorial on cyclohexane

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9
Q

Aromaticity

A

Huckel Rule: 4n + 2 (n is integer)

Aromaticity increase stability

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10
Q

Bronsted Lowry Acid-Base

A

Transfer of H+ from acid to a base
BL acid - compound w/ a H+ that can be lost
BL base - e- available to bind to an H+
As an acid gets stronger it has a weaker conjugate base

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11
Q

Lewis Acid-Base

A

Transfer of e- pair from base to acid
Lewis bases are nucleophiles
Stength of an acid depends on intramolecular forces
-Acid is stronger w/ an e- withdrawing group

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12
Q

Hydrogen Bonding

A

Weak bond
Bond btw lone pair of e- and hydrogen w/ partial (+) charge
No H bonding on H’s bonded to carbons

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13
Q

Van der Waals Forces

A

Exist btw all compounds
Considered only when no other factors
btw temporary dipoles

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14
Q

Constitutional Isomer

A

Same formula, different connectivity

Finite # of constitutional isomers for a formula

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15
Q

Cycloalkanes

A

Farther from 109.5 degree angle, the greater the strain and reactivity

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16
Q

Index of Hydrogen Deficiency

A

Alkanes - C(n)H(2n+2)

IHD = 2(#C) + (#N) - (#H) - (#X) +2 /2

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17
Q

IR Spectroscopy

A 
Finds functional groups
OH - broad at 3600
NH - 3400-3200 (medium)
Ketone - ~1700 (strong)
Aldehyde - ~1740 (strong)
Aromatic - 1600-1400
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18
Q

NMR

A

Takes advantage of hydrogen nucleus magnetic spin

Determines unique hydrogens

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19
Q

Meso Compounds

A

Have opposing chiral centers, therefore optically inactive

Contain mirror plane through an even # of chiral centers

20
Q

Stereoisomerism

A 
# of stereoisomers = 2^n
-less if some are meso
21
Q

Nucleophilic Substitution

A

Substitution of one functional group for another
Nucleophile attacks the electrophile
Sn1 or Sn2

22
Q

Nucleophile

A

Smaller nucleophiles are better
Nuc strength is correlated to base strength
Therefore small strong bases are good nucleophiles (but OH and OR can induce elimination)

23
Q

Electrophile

A

Strength is correlated to stability of LG
Good LG is stable in solution
Good LG has weak bond w/ carbon
I > Br > Cl&raquo_space; F

24
Q

Sn2 Reaction

A 
Nuc attacks backside and pushed LG out
Causes inversion at chiral carbon
One step reaction
rate = k[Nuc][Elec]
Sn2 favors primary > secondary > tertiary
Doesn't form a racemic mixture
25
Q

Sn1 Reaction

A 
LG leaves before Nuc attacks
Does not depend on Nuc concentration
Forms carbocation intermediate
Favored tertiary > secondary > primary (no methyl)
Favored in poor nucleophile
rate = k[Elec]
Slow two step reaction
Forms a racemic mixture
Carbocations can rearrange to form tertiary
26
Q

Free Radical Halogenation

A

Halogen bond is cleaved to form halogen radicals
Hydrocarbon radical stability: tertiary > secondary > primary > methyl
Mech: 1) initiation; 2) propagation; 3) termination
Selective forming tertiary alkyl halogens (favors substituted product)

27
Q

E2 Reaction

A

Carried out under basic conditions at high temperature
Occurs in one step
Requires a bulky base; prevents nuc addition
Substituents must be anti
Yields most substituted alkene

28
Q

E1 Reaction

A

Carried out under acidic condition at high temp

Forms a carbocation intermediate (therefore possible rearrangement)

29
Q

Hofmann Elimination

A

Forms least substituted alkene

Uses a quaternary amine

30
Q

Alcohols

A

Higher boiling points and miscibility in water
Become less hydrophilic as carbons are added
As branching increases, boiling point decreases
As molecular mass increases, boiling point increases
Not good as Nuc, must be deprotonated to an alkoxide

31
Q

Aldehydes and Ketones

A 
Don't form H-bonds
Only slightly miscible in water
Reactivity: at electrophilic carbon
Ald: IR - 1720-1740; NMR - 9-10
Ket: IR - 1710-1725; NMR - 2.0-2.5
32
Q

Carbonyl Reactivity

A

Attack at carbonyl group
C=O, carbon is good electrophile
Reactivity:
Acid halide > Acid anhydride > ester > amide

33
Q

Aldol Condensation

A

Kinetic Product - major product minimizes steric hindrance of TS
-chooses least substituted alpha carbon (low T, bulky base)
Thermo Product - maximizes stability of intermediate or product
-choose more substituted alpha carbon (high T, small base)

34
Q

Epimers

A

Vary in chirality at most oxidized C

Sugar diastereomers at one chiral center

35
Q

Anomers

A

Vary in chirality of least oxidized C
Diastereomers of the cyclic form (alpha or beta)
Beta - Up; alpha - down

36
Q

Osazome Test

A

Epimers yield the same osazome

Helps determine identity of sugar

37
Q

Tollens Test

A

Reduction of silver by oxidizable sugar

(+) test if silver mirror forms quickly, indicative of an aldose

38
Q

Amine Basicity

A

Secondary > Primary > Tertiary > NH3
Amines are increasingly nucleophilic w/ more alkyl groups
Therefore primary amines are hard to synthesize

39
Q

Distillation

A

Removes a liquid from another liquid by explooiting differences in boiling point
Fractional Distillation is used when liquids have small boiling point differences

40
Q

Thin Layer Chromatography

A

Spot sample on silica gel
Solvent moves up plate interacting w/ samples
Use Rf values for spots of the compounds
-High Rf indicates most solubility in solvent (most like solvent)

41
Q

Column Chromatography

A

Separate bulk quantities of product

If a compound travels quickly, then minimal attraction to stationary phase

42
Q

Gas Chromatography

A

Vaporize sample into gas phase
Heavier gases move slower and have longer elution times
-b/c heavy and polar gases have higher point and also have longer elution times (therefore lower boiling point compounds come off GC first)

43
Q

Extraction

A

Works on solubility
-Takes advantages of drastic solubility differences
Acid-Base:
Separate components on pH
-Loss of charge favors organic (uncharged polar); gain of charge favors water (protonation)
-Brine solution is used to increase differences in aqueous and organic layers

44
Q

Recrystallization

A

Solid product separated from solid impurities through selective precipitation
Dissolve solid into hot solvent, filtering out insolubles, then cool solution to precipitate purified crystals
Use minimal solvent so soluble at high temps and insoluble at low temps

45
Q

Mixed Melting Temperature

A

A mixture of compounds has a broader melting point indicating impurities

MCAT Organic Chemistry (1 decks)

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