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Chemistry (S2) > 2.7 Reaction Mechanisms > Flashcards

2.7 Reaction Mechanisms Flashcards

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1
Q

What does the mechanism of an organic reaction show?

A

How electrons move around to break bonds and make new ones
(Can be single or multiple steps)

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2
Q

What is a kinetic product?

A

The one with the lowest Ea

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3
Q

What is the thermodynamic product?

A

The most stable

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4
Q

What mechanism is where bonds break involving the movement of a single electron?

A

Free radical mechanisms
Produce radical intermediates (1 unpaired electron) - very reactive

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5
Q

How is the movement of a single electron shown?

A

A curly arrow with a single head (fish hook arrow)

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6
Q

What are the characteristics of bonds that break into radicals?

A

Tend to be non-polar
Energy input required to break bond
This can be in form of heat or light (uv)

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7
Q

How is two radicals pairing up illustrated in a mechanism?

A

Two single headed arrows come together to create an electron pair

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8
Q

What are the steps of a free radical mechanism?

A

Initiation: free radical formation - more radicals on right of equation

Propergation: same number of radicals on either side of reaction

Termination: when 2 radicals pair to form an unreactive molecule

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9
Q

What enzymes use free radicals in their mechanisms to functionalise biological molecules?

A

Prostaglandin - start from arachidonic acid - tyrosine side chain radical

Fatty acids double bonds - introduced with iron cofactor

Metabolism of drugs/steroids - rely on iron cofactor (which creates radical)

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10
Q

How does water form radicals

A

OH bonds split to give hydroxy radical - causes aging

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11
Q

Give an example of a vitamin that uses free radicals

A

Vitamin E - antioxidants

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12
Q

What does a polar/Ionic mechanisms show?

A

Movement of pairs of electrons - indicated by double headed curly arrow

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13
Q

What direction do electrons tend to go in?

A

Direction of most electronegative atom

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14
Q

What are electrophiles?

A

Electron-loving
Short of electron - what to gain
Will have a + charge or a partial positive charge

Eg. Cations, carbonation

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15
Q

What are nucleophiles?

A

Electron rich
Might be - charged, partially negativity charged, or have lone pair of electrons

Eg. Anions, carbanions
O, N

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16
Q

What is an adition reaction?

A

Where a small molecule is incorporated into a larger starting material

17
Q

What is a classic feature of addition reactions?

A

Pi bond broken in starting material
2 new sigma bonds formed as reagent added to starting material

(Happens in molecules with double bonds)

18
Q

What are electrophilic and nucleophilic addition reactions?

A

Electrophilic - double bond is attached by electrophilic agent

Nucleophilic - double bond attached by a nuceophilic agent

19
Q

Give an example of a nucleophic addition reaction

A

fumaric acid ——-> malic acid

O: in water acts as nuceophile
Catalysed by fumarase

20
Q

What is an elimination reaction?

A

The reverse of an addition reaction
2 sigma bonds are broken to form a pi bond

21
Q

Give an example of an elimination reaction

A

2-phophoglycerate ——->phosphoenolpyruvate

Water is being removed
Catalysed by Enolase enzyme

22
Q

What 2 type of reactions can be seen as special cases of addition and elimination?

A

Oxidation and reduction

Reduction - usually addition of a hydrogen (H2) molecule

Oxidation - usually elimination/removal of H2 molecule

23
Q

What are condensation reactions?

A

Joining 2 molecules together. Often involves removal of small molecule.

Biologically usually H20
Chemistry can be things like HCl

24
Q

Give examples of condensation reactions

A
  1. Formation of peptides/proteins
  2. Formation of esters (carboxylic acid + alcohol)
  3. Formation of nucleosides
  4. Formation of phosphate esters
25
Q

What is a substitution reaction?

A

Where a functional group is directly replaced by another one

26
Q

What are the 2 types of substitution reactions?

A

Nucleophilic - more biological relevant - happens on sp3 hybridised C atoms - polar bond is attacked by nucleophile and replaces

Electrophilic - characteristic reaction of aromatic rings - allows to maintain stability

27
Q

What is a rearrangement (isomerisation) reaction?

A

Formula of molecule doesn’t change, but arrangement of atoms in space does

28
Q

Example of rearrangement reaction

A

Succinyl CoA ——-> (R)-Methylmalonyl CoA

Catalysed by methylmalonyl-CoA mutase

Chemistry (S2) (9 decks)

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