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Organic Chemistry > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

(ΔG) Gibbs Free Energy

(Basic Definition and Types of Reaction)

A

Ultimate Determinant for whether a reaction will happen

(+) Endergonic reaction (unfavorable)

(-) Exergonic reaction (favorable)

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2
Q

(TΔS) Entropy

(Basic Definition and Reaction Types)

A

“Disorder”/ Change in number of molecules

(+ΔS)= favorable

(-ΔS) = unfavorable

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3
Q

(ΔH) Enthalpy

(Basic Defintion and Reaction Types)

A

bonds breaking/ forming

(+) = Endothermic Rxn (unfavorable)

(-) = Exothermic Rxn (favorable)

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4
Q

Enthalpy (ΔH or q)

Definition

A

The heat energy exchange between the reaction and it surroundings

Breaking a bond (bond cleavage) requires the system to absorb energy

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5
Q

Bond Cleavage

(Two Types)

A
  • Homolytic: occurs with equal sharing of electrons. Forms two uncharged radicals
  • Heterolytic: unequal splitting/ sharing of electrons. Forms two ions
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6
Q

Bond Dissociation Energy (BDE)

A

or ΔH for bond breaking refers to homolytic cleavage

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7
Q

How do you calculate the heat of reaction?

A

can calculate by subtracting BDEs for bonds formed from the sum of BDEs of bonds broken.

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8
Q

Entropy ΔS

A
  • exothermic and endothermic rxns can occur spontaneously
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9
Q

What two factors most significantly affect ΔS and make it positive?

A
  1. When there are more moles of product than reactant
  2. When a cyclic compound becomes acyclic
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10
Q

ΔG

A
  • Gibbs Free Energy
  • A negative value of G means the reaction is spontaneous
  • A positive value is nonspontaneous
  • temperature sensitive
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11
Q

Negative ΔG

A

Spontaneous, Exergonic

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12
Q

Positive ΔG

A

non spontaneous, endergonic

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13
Q

Spontaneous Reaction

A
  • ΔG < 0
  • [products]>[reactants]
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14
Q

Keq

A

Keq=[products/reactants]
- Keq>1, the rxn favors the products
- Keq <1, the reaction favors the reactants

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15
Q

What are the five factors that influence reaction kinetics?

A
  1. concentrations of the reactants
  2. activation energy
  3. temperature
  4. Geometry and sterics
  5. presence of a catalyst
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16
Q

What does the reaction constant k depend on?

A

the activation energy, temperature, and sterics
larger k = faster rate

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17
Q

Catalyst

A
  • speed up a reaction but are not consumed in the process
  • act to decrease the activation energy (altering kinetics) but having no impact on the delta G
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18
Q

Transition States

A
  • fleeting existence, cannot be isolated
  • represents every maxima, point of bonds breaking/forming
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19
Q

Hammond Postulate

A
  • For an exothermic reaction, transition state resembles reactants
  • For an endothermic reaction, transition state resembles products
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20
Q

Nucleophile

A
  • electron rich species, can donate a pair of electrons
  • Lewis bases (carry a lone pair of electrons)
  • More polarizable nuleophile=stronger nucleophile
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21
Q

Electrophile

A
  • electron deficient species
  • can accept a pair of electrons
  • Lewis acids
  • Carbocations and partially positive atoms are electrophilic
22
Q

What is the purpose of a reaction mechanism?

A

Stepwise description of chemical reactions

23
Q

What are the four major types of arrow pushing patterns?

A
  • nucleophilic attack
  • Loss of a leaving group
  • proton transfer
  • carbocation rearrangement
24
Q

Nucleophilic Attack

A

the electron pusing arrow starts at the nucleophile and points towards the electrophile

25
Q

Loss of a Leaving Group

A

Electrons from a bond relocate to the departing atom/group

26
Q

Proton Transfer

A

Any time hydrogen is moving around, likely a proton transfer

27
Q

Carbocation rearrangements

A
  • positive charge on a carbon is stabilized by having more alkyl groups around (hyperconjugation)
28
Q

Methyl Shift or Hydride Shift

A

methyl groups or hydrogens can rearrange to produce a more stable carbocation

29
Q

Hyperconjugation

A

having more electron density near by (more stuff) stabilizes a (+) charge

30
Q

Two major types of organic reactions

A

substitution and elimination
- frequently involving alkyl halides

31
Q

Alkyl Halides

A
  • aka haloalkanes or organohalides
  • great for substitution because:
  • the carbon adjacent to the halogen is electrophilic
  • Some halogens are great leaving groups (conjugate base of a strong acid)
32
Q

Sn2 Reactions

A

a bimolecular substitution reactoin that has a concerted mechanism
- Rate=k[alkyl halide][nucleophile]

33
Q

alpha carbon

A
  • ## the electrophile attached to the halogen
34
Q

What happens if the alpha carbon is a chiral center?

A

the steriochemistry is inverted

35
Q

What is the effect of more substitution on the alpha and beta carbons?

A

It decreases the reactivity of the alkyl halide.

3 prime is unreactive, 1 prime is most reactive

36
Q

What is Nucleophilicity?

A

the rate at which a nucleophile will attack an electrophile
- strong nucleophile needed for SN2 Reaction

37
Q

E2 Reaction

- What happens
- Outcome
- Reaction Rate

A
  • favored in the presence of a strong base (OH-, OEt -, t-BuO-)
  • Alkyl halides lose both the halogen and a hydrogen from the beta carbon in a process called B elimination
  • Outcome: double bond between alpha and beta carbon
  • Rate=k[strong base][alkyl halide]
  • prefers more substituted alkyl halides
38
Q

Stability of Alkenes

A
  • trans alkenes are more stable than cis
  • more substituted alkanes are more stable to due hyperconjugation (stabilizing the electrons in the double bond)
39
Q

What is regiochemistry?

A

an area of a reaction where the changes occur

40
Q

What is regioselective?

A

reaction favors one direction/location for the reaction to occur on the molecule

41
Q

Zaitsev Product

A
  • double bond forms towards the MORE substituted side (more stable product)
  • Favored by using small, strong bases
  • Ex: (OH-, OEt-)
42
Q

Hoffman Product

A
  • Double bond forms towards the Less substituted side (less stable product)
  • Favored by using big, bulky bases (t-BuO-)
43
Q

Stereoselectivity

A
  • When there is more than one beta hydrogen on the same carbon, can form cis or trans product
  • selective for trans product
44
Q

Stereospecific

A
  • If there is only one beta hydrogen, only one product can form
  • Double bond forms when the halogen and beta hydrogen are coplanar or periplanar (aligned in space)
45
Q

What type of mechanism is SN2 and E2 reactions

A
  • concerted mechanism, one step
46
Q

What type of mechanism is SN1 and E1

A

multistep mechanism

47
Q

What is solvolysis?

A
  • a reaction with a solvent
48
Q

What are some traits of SN1 and E1 reactions?

A
  • primarily seen with tertiary alkyl halides
  • frequently a reaction with a solvent
  • proceeds through a carbocation intermediate
  • unimolecular kinetics
  • Rate=[alkyl halide]
49
Q

What is unimolecular kinetics?

A

a rate that depends on the concentration of only one reactant

50
Q

What type of reaction does heat favor?

A

elimation reaction

Organic Chemistry (10 decks)

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