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MCAT OChem > Hydrocarbons, Alcohols, and Substitutions > Flashcards

Hydrocarbons, Alcohols, and Substitutions Flashcards

1
Q

methyl, primary, secondary, tertiary, qaternary carbons on alkanes

A

methyl - bonded to chain with no other carbons
primary - bonded to one other carbon/bonded to the chain and one other carbon
secondary - 2…
tertiary - 3…

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2
Q

boiling point properties of alkanes

A

increase as carbons added - molecular weight and intermolecular forces increase
branching lowers boiling point

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3
Q

melting point properties of alkanes

A

increases with increasing molecular weight

branching increases melting point

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4
Q

density of alkanes

A

lowest density of all groups

density increases with molecular weight

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5
Q

alkane solubility

A

almost totally insoluble in water
soluble in benzene, carbon tetrachloride, chloroform, and other hydrocarbons
if alkane contains polar functional group, polarity and solubility of molecules decreases as carbon chain is lengthened

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6
Q

alkanes of four carbons or less are ___ at room temp

A

gases

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7
Q

ring strain is zero for….

A

cyclohexane, increases as rings become larger and smaller

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8
Q

the ___ conformer of cyclohexane predominates

A

chair - lowest energy

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9
Q

equatorial hydrogens

A

hydrogens projecting outward from the center of the ring

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10
Q

axial hydrogens

A

projecting upward or downward in ring

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11
Q

when ring reverses its conformation, all the hydrogens….

A

reverse their orientation (equatorial axial)

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12
Q

large substituents in axial position…

A

crowding occurs, raises energy level –> less stable

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13
Q

combustion

A

when alkanes are mixed with oxygen and energy is added
high temps (inside flame)
radical reaction
CH4 + 2O2 –> CO2 + 2H2O +heat

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14
Q

heat of combustion

A

change in enthalpy of a combustion reaction

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15
Q

the higher the heat of combustion, the higher the…

A

higher the energy level of the molecule, less stable

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16
Q

Alkanes will react with halogens in the presence of heat or light to form a ___ ___

A

free radical: highly reactive species with unpaired e-

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17
Q

halogenation

A
  1. initiation: halogen starts as diatomic molecule, homolytically cleaved by heat or light –> 2 free radicals
  2. propagation: halogen radical removes H from the alkane –> alkyl radical. alkyl radical reacts with diatomic halogen –> alkyl halide and new halogen radical
  3. termination: 2 radicals bond or a radical bonds to the wall of the container to end the chain reaction or propagation
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18
Q

reactivity of halogens from most reactive to least

A

F, Cl, Br, I

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19
Q

___ are more acidic than ____

A

alkenes are more acidic than alkanes

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20
Q

the more highly substituted the alkene, the more ____

A

the more thermodynamically stable

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21
Q

elimination reaction –>

A

alkene

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22
Q

dehydration of an alcohol

A

E1 reaction, alcohol forms an alkene in presence of hot concentrated acid

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23
Q

E1

A

rate depends upon concentration of only 1 species

carbocations

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24
Q

carbocation stability

A

most: tertirary, secondary, primary, methyl : least

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25
Saytzeff rule
the major product of elimination will be the most substituted alkene
26
dehydrohalogenation
E1 (absence of strong base) or E2 (high concentration of strong bulky base)
27
E2 dehydroghalogenation
1 step | base removes a proton from the carbon next to the halogen containing carbon, halogen drops off leaving alkene
28
nucleophile
electron rich compound, donate an e pair to form covalent bond
29
syn addition
same side addition | in catalytic hydrogenation
30
electrophilic addition
important reaction for alkenes 1: H of hydrogen halide acts as electrophile, adds to doulbe bond via Markvonikov's rule. rate determining slow step 2. new carbocation picks up negatively charged halide ion
31
electrophile
electron loving species, at least partial positive charge
32
double bond of alkene will attract ....
electrophiles, is an e- rich environment
33
Markovnikov's rule
the hydrogen will add to the least substituted carbon of the double bond -when hydrogen halides are added to alkenes, in electrophilic addition reactions
34
anti-Markovnikov addition
is peroxides are present, the bromine (not the H) will add to the least substituted carbon
35
hydration of an alkene
water added to an alkene in presence of acid, follow Markovnikov's rule, low temps and dilute acid --> alcohols
36
anti-addition
addition from opposite sides of double bond
37
halogenation of an alkene
add one to each C of double bond
38
benzene only undergoes ___ reactions
substitution, not addition
39
benzene is a ____ molecule stabilized by ____
flat molecule stabilized by resonance
40
if benzene has one substituent, remains 5 positions labeled....
ortho (2 closest) , meta (next 2), para (1)
41
SN1 reaction
2 steps 1. formation of carbocation, slow rate determining step, leaving group leaves 2. nucleophile attacks he carbocation
42
the rate determining step of SN1 is independent of of the concentration of the ____ and is directly proportional to the concentration of the ____
independent of nucleophile, proportional to concentration of substrate (elecrophile or molecule being attacked by the nucelophile)
43
SN2 reactions
1 step, rate dependent on concentration of nucleophile and substrate nucleophile attacks substrate from behind leaving group, knocks leaving group free while bonding to the substrate
44
inversion of configuration for SN2
inversion of configuration on the carbon being attacked by the nucleophile
45
SN2 reactions don't typically occur with ____ substrates
tertiary substrates, tertiary carbon would sterically hinder the nucleophile
46
nucleophile SN1 vs. SN2
SN2 requires a strong nucleophile, nucleophile strength doesn't affect SN1
47
Substrate for SN1 vs. SN2
SN1: secondary or tertiary substrate SN2: methyl, primary, or secondary; don't occur w/ sterically hindered substrates
48
solvent for SN1 vs. SN2
highly polar solvent increases rate of SN1 by stabilizing carbocation, slows SN2 by stabilizing nucleophile
49
speed of SN1 vs. SN2
speed of SN2 depends on concentration of substrate and nucleophile, speed of SN1 depends on concentration of just substrate
50
stereochemistry of SN1 vs. SN2
SN2 inverts stereochemistry about chiral center, SN1 creates racemic mixture
51
carbon skeleton rearrangement SN1 vs. SN2
SN1 may rearrange, SN2 never rearranges carbon skeleton
52
elimination occurs when the nucleophile behaves....
as a base rather than a nucleophile : abstracts proton rather than attacking carbon
53
alcohols follow same trend as alkanes, but boiling and melting points are higher due to ____
hydrogen bonding - increases the intermolecular forces which must be overcome to change phase
54
alcohols are much _____ soluble in water than alkanes and alkenes
alcohols are much more soluble in water - hydroxyl group increases polarity longer the carbon chain, the less soluble
55
order of acidity of alcohols
strongest : methyl, primary, secondary, tertiary : weakest
56
Grignard Synthesis of an alcohol
with organometallic compound, C attacks C with double bonded O, O accepts H
57
Grignard reagents will react with ______ and can deprotonate ____
react with: C=N , C=-N, S=O, N=O | deprotonate: O-H, N-H, S-H, C=-C-H
58
alcohols like to act as....
nucleophiles, nucleophilic addition or substitution
59
___ and ___ alcohols can be oxidized
primary and secondary alcohols
60
oxidation:
loss of H2, addition of O or O2, addition of X2 (halogen)
61
reduction
additions of H2 or H-, loss of O or O2, loss of X2
62
neither oxidation or reduction
additions or loss of H+, H2O, HX
63
oxidizing agents will have lots of ____
oxygen
64
reducing agents will have lots of ___
hydrogen
65
formation of alkyl halide from alcohol
OH group attackes H from HX --> water | X- attacks C and water leaves
66
alcohols form esters called
sulfonates: very weak bases and excellent leaving groups, used to protect alcohols
67
formation of sulfonates
nuceleophilic substitution, alcohol acts as nucleophile, retention of configuration
68
tosylates and mesylats
commonly used sulfonates
69
pinacol rearrangement
dehydration of an alcohol that results in an unexpected product, ultimately forms pinacolone and regenerated acid catalyst
70
____ and relativerly non-reactive
ethers
71
___ is almost always the anser to sollvent questions
Ether - relatively low boiling point, roughly as soluble in water as alcohols, organic compounds tend to be more soluble in ethers because no H bonds need to be broken
72
ethers are cleaved by....
cleaved by HI and HBr to form alcohol and alkyl halide | R-O-R + HBr --> ROH + RBr
73
epoxides
three membered cyclic ethers | react with water in presence of acid to from diols called glycols with anit-addition

MCAT OChem (4 decks)

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