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1.2 Organic Chemistry > Reaction Mechanisms - Addition of Alkenes + Equilibrium > Flashcards

Reaction Mechanisms - Addition of Alkenes + Equilibrium Flashcards

1
Q

What is the most common reaction of alkanes?

A

Substitution

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2
Q

What is the general formula for the substitution for alkanes?

A

R-H + A-B = R-A + H-B

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3
Q

R-H + A-B = R-A + H-B

What is H substituted with?

A

H is substituted with A

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4
Q

R-H + A-B = R-A + H-B

What is B in this?

A

The LG -> limiting?

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5
Q

What is the most common reaction of alkenes?

A

Addition

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6
Q

What is the general formula for the addition of alkenes?

A

C=C + A-B = C-C(A-B -> drawn bellow in molecular formula))

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7
Q

What three things can be added to alkenes by a two step polar process?

A

Addition of halogens

Addition of water (hydration)

Addition of acids

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8
Q

What happens in the addition of halogens?

3

A

Cl2 and Br2 can be added readily

Happens nearly instantaneously even at room temperature or below

No light or heat is required

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9
Q

Name two halogens that can be readily added to alkenes?

A

Cl2

Br2

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10
Q

What is not needed for the addition of halogens?

2

A

Light

Heat

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11
Q

Heat is not needed for the addition of halogens, what is this similar to?

A

Similar to the substitution of alkanes

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12
Q

What happens in the addition of water?

2

A

An acid catalyst is required because a neutral H2O molecule is not acidic enough to provide protons to start the reaction

Its a multistep mechanism

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13
Q

What is needed in the addition of water?

A

An acid catalyst

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14
Q

Why is an acid catalyst needed in the addition of water?

A

Because a neutral H2O molecule is not acidic enough to provide protons to start the reaction

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15
Q

What is needed to start the reaction of hydration?

A

Protons

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16
Q

What happens in the addition of acids?

3

A

This applies a variety of acids

The first step involves the addition of a H+ to the C=C bond

X- is then added (acid with negative charge)

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17
Q

How many products can be formed using a symmetric reagent and/or alkene?

A

One one addition product is possible

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18
Q

How many products can be formed using an unsymmetrical reagent/and or alkene?

A

Two products are possible

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19
Q

What are regioisomers?

A

Isomers which have the same functional groups but attached at different positions

20
Q

What is it called if an addition reaction involving both an unsymmetric alkene and reagent MAINLY only gives one regioisomer?

A

The reaction is said to be regioselective

21
Q

Most reagents used in addition reactions are polar, what does this mean?

A

There is a + and a - end

e.g. H+Cl-

22
Q

What is the Markovnikov rule?

2

A

When an unsymmetrical reagent adds to an unsymmetrical alkene

The electropositive part of the reagent bonds to the C of the C=C that has the greater number of H atoms attached to it

23
Q

What does the Markovnikov rule apply to?

A

When an unsymmetrical reagent adds to an unsymmetrical alkene

24
Q

What are electrophiles?

4

A

Electron lovers

They are electron poor reagents

They seek electrons

They are often + ions (cations) or otherwise electron deficient species

25
Q

What are electrophiles often?

A

Cations

+ ions

26
Q

What are nucleophiles?

3

A

Nucleus lovers

They are electron rich

They form bonds by donating electrons to an electrophile

27
Q

In what direction do the electrons travel when a bond is formed between a nucleophile and an electrophile?

A

The nucleophile donates electrons to an electrophile

arrow goes from nucleophile to electrophile

28
Q

What is a carbocation?

3

A

An ion with a positively charged carbon atom

A carbonium ion

An organic cation in which the positive charge is located on a carbon atom

29
Q

Why are carbocations highly reactive?

2

A

The Carbon lacks electrons (only has 6)

The carbon will therefore react with any species that will provide it with 2 electrons (e.g. Nu-)

30
Q

What is usually the first stage in an addition reaction?

A

The formation of the carbonium ion

31
Q

Why is the formation of the carbonium ion the slowest step of addition?

A

This is because once the carbonium ion is formed it will react quickly to gain 2 electrons

32
Q

What is the first step in all addition reactions?

A

Attack by the electrophile

33
Q

Since attack by the electrophile is the first step what is the overall process often called?

A

Electrophile addition reaction

34
Q

What is chemical thermodynamics?

2

A

The changes in energy that take place when chemical reactions occur

Thermodynamics control the extent to which a reaction goes to completion

35
Q

What is chemical kinetics?

A

The velocity or rate at which the concentrations of reactants and products change

36
Q

What is a state of equilibrium?

A

When the concentrations of reactants and products no longer change

37
Q

When is a reaction said to go to completion?

A

When equilibrium lies extensively (>99.9%) on the side of the products

38
Q

What does the equilibrium constant tell us?

A

The direction that is favoured by the system

39
Q

What does it mean if Keq > 1?

A

The formation of the products C and D will be favoured

40
Q

What does it mean if Keq < 1 ?

A

The preferred direction for the reaction is from right to left (A+B) is favoured

41
Q

What is the equation for Keq?

A

Keq = ([C]^c[D]^d)/([A]^a[B]^b)

42
Q

What happens when products are lower in energy (more stable) than the reactant?
(2)

A

Heat will be given off in the reaction

An exothermic reaction

43
Q

When will an exothermic reaction occur?

A

When the products are lower in energy (more stable) than the reactants

44
Q

What is enthalpy?

A

The term for heat energy associated with a chemical reaction

45
Q

What is the difference in enthalpy between products and reactant called?

A

Delta H

1.2 Organic Chemistry (15 decks)

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