Transcript H + - uaschemistry

ORGANIC OPTION -G
IB Core Option Objective
Electrophilic Addition Reactions
• G.1.1 Describe and explain the
electrophilic addition mechanisms of the
reactions of alkenes with halogens and
hydrogen halides.
Terms
• Electrophile:
• Carbocation:
• Carbocation stabalization:
• Nucleophile: (Loves positives) Any molecule
or ion that has a lone pair of electons
G.1.1 Describe and explain the electrophilic addition
mechanisms of the reactions of alkenes with halogens
and hydrogen halides.
• Alkene double bond is attacked by an
electrophile
Cl
–
Cl
Cl
+
C
H
C
H
1-Chloroethane
IB Core Option Objective
• G.1.2 Predict and explain the
formation of the major product in
terms of the relative stabilities of the
carbocations.
G.1.2 Predict and explain the formation of the major product
in terms of the relative stabilities of the carbocations.
• Markovnikov’s Rule
– H-X when added to a multiple bond molecule,
hydrogen will always add to the carbon with the
most hydrogen's.
Primary
Secondary
Increasing stability
Tertiary
Carbocation stabilization
• Iodine monochloride:
– Identify the more electronegative group
– Is the molecule polar?
– Draw the steps for how the product is formed, and
name the product.
Iodine monochloride + propene
IB Core Option Objective
Nucleophilic Addition Reactions
• G.2.1 Describe, using equations, the addition
of hydrogen cyanide to aldehydes and
ketones.
• G.2.2 Describe and explain the mechanism for
the addition of hydrogen cyanide to aldehydes
and ketones.
G.2.1 Describe, using equations, the addition of hydrogen
cyanide to aldehydes and ketones.
• HCN + OH-  H2O + CN- (Requires a base catalyst
to make CN- which is a better nucleophile)
• Significance: Increases carbon chain length by one carbon
Cyanide ion + Propanone
G.2.1 Describe, using equations, the addition of
hydrogen cyanide to aldehydes and ketones.
Which end is
slightly positive
and negative?
O
O
C
C
R
R
R
• Draw the VSEPR diagram for CN-
H
G.2.2 Describe and explain the mechanism for the addition of
hydrogen cyanide to aldehydes and ketones.
• CH3CHO + HCN with OH• Get in partners, use the molecular model kits
and make the structures for each.
• Play out the steps for this reaction in pairs.
• While working the steps in 3D, show the steps
for this reaction on paper, showing the
intermediate step and the product. Use curly
arrows to show electron transfer.
IB Core Option Objective
• G.2.3 Describe, using equations, the
hydrolysis of cyanohydrins to form
carboxylic acids.
G.2.3 Describe, using equations, the hydrolysis of
cyanohydrins to form carboxylic acids.
• The Nitrogen group can be removed by:
– 1) Adding a base to produce carboxylic acid & NH3
– 2) By adding an acid to produce NH4+
R
C
N
O
O
R
C
OH NH +
4
R
C
O
NH3
G.2.3 Describe, using equations, the hydrolysis of
cyanohydrins to form carboxylic acids.
Hydrolysis
• Take the product you made from the previous
reaction (2-hydroxypropanenitrile) and react it
with water and acid. What are your products?
• A: 2-hydroxypropanoic acid (lactic acid) and
NH4+.
G.2.3 Describe, using equations, the hydrolysis of
cyanohydrins to form carboxylic acids.
H
C
C
H
H
H
H
H
C
H
C
C
H
H
H
H
IB Core Option Objective
• G.4.1 Describe, using equations, the
reactions of 2,4-dinitrophenylhydrazine
with aldehydes and ketones.
G.4.1 Describe, using equations, the reactions of 2,4dinitrophenylhydrazine with aldehydes and ketones.
• Addition: 2,4 –dinitrophenylhydrazine acts as
a nucleophile (non-bonding pair of electrons).
• Elimination: The two hydrogens bonded to
the nitrogen will bond with the oxygen on a
ketone or aldehyde, causing atoms to be
eliminated to form water.
NO2
H
H
N
N
H
NO2
G.4.1 Describe, using equations, the reactions of 2,4dinitrophenylhydrazine with aldehydes and ketones.
Significance: Creates an orange-yellow
precipitate which can be melted to test
what ketones or aldehydes are present
in solution based on its MP.
NO2
NO2
H
H
N
N
+
Propanone
H
Note: Products from these reactions are called 2,4-dinitrophenylhydrazones. You do not
need to know how to name specific products for this reaction.
You don’t need to know every step!
G.4.1 Describe, using equations, the reactions of 2,4dinitrophenylhydrazine with aldehydes and ketones.
IB Core Option Objective
• G.3.1 Describe, using equations, the
dehydration reactions of alcohols with
phosphoric acid to form alkenes.
• G.3.2 Describe and explain the
mechanism for the elimination of water
from alcohols.
G.3.1 Describe, using equations, the dehydration
reactions of alcohols with phosphoric acid to form alkenes.
• What would the equation be for the
dehydration of ethanol?
• A: C2H5OH → C2H4 + H2O
• What would be needed to protonate the
hydroxyl group? Is it a catalyst or part of the
products?
• A: Strong acid, preferably phosphoric (V) acid,
H3PO4. It is a catalyst, since a proton is
donated back to regenerate the acid.
G.3.2 Describe and explain the mechanism for the
elimination of water from alcohols.
Dehydration of alcohols to form alkenes using
acids.
Concentrated
phosphoric acid
Butan-1-ol
180 oC
Concentrated
phosphoric acid
Butan-2-ol
180 oC
G.3.2 Describe and explain the mechanism for the
elimination of water from alcohols.
Mechanism
Butan-1-ol
Phosphoric acid
H
Conjugate Base
O
Carbocation
PO3H2
Carbocation
Butene
IB Core Option Objective
• G.5.1 Describe and explain the structure
of benzene using physical and chemical
evidence.
• For physical evidence, include a comparison of carbon–
carbon bond lengths in alkanes, alkenes and benzene, and
the number of structural isomers with the formula C6H4X2.
• For chemical evidence, include a comparison of the
enthalpies of hydrogenation of benzene, cyclohexene,
1,3-cyclohexadiene and 1,3,5-cyclohexatriene, and the
tendency of benzene to undergo substitution rather than
addition reactions.
G.5.1 Describe and explain the structure of
benzene using physical and chemical evidence.
What do you know?
You already know some things about benzene.
Brainstorm with a partner what you already
know! Think back to Topic 4 or 10!
G.5.1 Describe and explain the structure of
benzene using physical and chemical evidence.
• Arenes: Compounds that contain benzene ring.
• How do we know: Three separate double bonds
with localized electrons or resonance structure
with delocalized electrons?
OR
Arenes
Br
Br
• Evidence:
• 1) Will not react with bromine water
Booya double bond
I’m gonna
Whatreact
the?you
good!!
?
– Significance: There must be no double bonds
• 2) Six equal bond lengths
– Significance: No alternating double/ single
bonds as double bonds are shorter, single
bonds are longer.
• 3) Benzene is more thermodynamically
stable
– Significance: Combustion of cyclohexatriene
should result in more energy released then
predicted.
Double bonds are
shorter than
single!!!
G.5.1 Describe and explain the structure of benzene
using physical and chemical evidence.
4) There are no second structural isomers for
1,2 disubstituted benzene compounds. (There
is only one)
5) Look at the study guide for the enthalpy of
hydrogenation of cyclohexene. What would
you expect if you hydrogenated two more
double bonds, compared to what happens in
benzene?
IB Core Option Objective
• G.5.2 Describe and explain the relative
rates of hydrolysis of benzene
compounds halogenated in the ring and
in the side-chain.
• Only the reactions with the OH– ion will be assessed.
G.5.2 Describe and explain the relative rates of hydrolysis of
benzene compounds halogenated in the ring and in the side-chain.
• Arenes can be halogenated directly on the
benzene ring:
Br
• Or they can be halogenated on a side chain to
H
the ring:
C
H
Br
G.5.2 Describe and explain the relative rates of hydrolysis of benzene
compounds halogenated in the ring and in the side-chain.
• If it is on the side chain, it undergoes nucleophilic
substitution just like a halogenoalkane. What is
needed as a reagent and what would the
mechanism be?
H
?
+
A: Aqueous NaOH, SN2
C
H
Br
→
?
G.5.2 Describe and explain the relative rates of hydrolysis of
benzene compounds halogenated in the ring and in the side-chain.
• If the halogen atom is directly attached,
nucleophilic substitution does not occur, or it
Br
occurs very slowly.
• This is due to the dense cloud of electrons
surrounding the arene ring, thus the nucleophile is
repelled.
• It is also due to the stronger C-Br bond from the
benzene than the C-Br bond in halogenoalkanes.
IB Core Option Objective
• G.6.1 Outline the formation of Grignard
reagents.
• G.6.2 Describe, using equations, the
reactions of Grignard reagents with
water, carbon dioxide, aldehydes and
ketones.
G.6.1 Outline the formation of Grignard reagents.
• Using halides to create longer carbon chains by
Nucleophilic addition, particularly using electron
deficient carbons on ketones and aldehydes
• Grignard Reagents
Mg + R-X
δ-
δ+
R-Mg-X
Carbon anion formed due to the
electronegativity difference
between C-Mg
G.6.2 Describe, using equations, the reactions of Grignard
reagents with water, carbon dioxide, aldehydes and ketones.
–δ
H
H
C
H
+
H
Acid removes remaining
part of Grignard reagent
in the intermediate step
C
R --Mg--X
H+
H
R--Mg--X
H
δ+
H
δ-
Reactions and Products
• 1) R-Mg-Cl + CO2  R-COOH
– Carbon dioxide  Carboxylic acid
• 2) R-Mg-Cl + H2O  R-H + Mg(OH)Cl
– Ketone  Alkane
• 3) R-Mg-Cl + C=O  R-C-OH
– Methanal  Primary alcohol
• 4) R1-Mg-Cl + R2-CHO  R1-CH(R2)-OH
– Aldehyde  Secondary alcohol
• 5) R1-Mg-Cl + R2-CO-R3  R1-C(R2R3)-OH
– Ketone  Tertiary alcohol
Questions
• Mg + 1-Chloroethane
•
•
•
•
•
•
1)
2)
3)
4)
5)
6)
Grignard + Water 
Grignard + Carbon dioxide 
Grignard + Methanal 
Grignard + Propanal 
Grignard + Propan-2-one 
Make the Grignard 2-Chlorobutane
IB Core Option Objective
• G.8.1 Describe and explain the acidic
properties of phenol and substituted phenols
in terms of bonding.
• Review: If an acid has a weak conjugate base,
is it a strong or weak acid?
A: It is strong.
G.8.1 Describe and explain the acidic properties of phenol
and substituted phenols in terms of bonding.
• Phenols are weakly acidic, but stronger than
ethanol.
• This is because the negative charge on the
conjugate base can be spread out over the
entire benzene ring (resonance).
HO
O
Can you figure out the other resonance structures?
-
O
G.8.1 Describe and explain the acidic properties of phenol
and substituted phenols in terms of bonding.
• Negative charge can be spread even further when
nitro groups are added.
• They are electron withdrawing, leading to an even
weaker conjugate base.
• Thus, 2,4,6-trinitrophenol is a strong acid.
• A group that donates electrons, such as CH3, will
make the anion less stable (stronger conjugate
base) and the acid weaker.
• Q: What would the order of pKa, from largest to
smallest, be for ethanol, phenol, 2-methylphenol,
and 2,4,6-trinitrophenol?
• A: Ethanol: pKa=16, 2-methylphenol pKa = 10.26,
Phenol pKa=10.0, 2,4,6-trinitrophenol pKa=0.42
IB Core Option Objective
• G.8.2 Describe and explain the acidic
properties of substituted carboxylic
acids in terms of bonding.
G.8.2 Describe and explain the acidic properties of
substituted carboxylic acids in terms of bonding.
• The conjugate base of carboxylic acids has two
resonance forms.
-
O
H
C
O
-
O
H C
O
• Adding more methyl groups will have a positive
inductive effect, making the acid weaker.
• Adding electron withdrawing substituents such as
chlorine will make the acid stronger.
IB Core Option Objective
• G.8.3 Compare and explain the
relative basicities of ammonia and
amines.
G.8.3 Compare and explain the relative basicities of
ammonia and amines.
• Like ammonia, amines will act as weak bases
when dissolved in water:
R-NH2 + H2O
R-NH3 + OH-
• Alkyl amines are stronger bases than ammonia
(positive inductive effect).
• The longer the alkyl group, the more basic the
amine.
• The base strength increases from a primary
amine to a tertiary amine.
G.8.3 Compare and explain the relative basicities of
ammonia and amines.
• What would the equation be if ethylamine
reacted with hydrochloric acid?
• A: C2H5NH2 + HCl → C2H5NH3+Cl(ethylammonium chloride)
• What would happen if you were to react the
ethylammonium chloride with warm sodium
hydroxide?
• A: C2H5NH3+Cl- + NaOH → C2H5NH2 + NaCl + H2O
Advanced Question
• How can you make 2,3 dimethyl-pent-3-ol
– Using only Propan-1-ol and Butan-1-ol
•
•
•
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•
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•
Press for hint # 1
Press for hint # 2
Press for hint # 3
Press for hint # 4
Press for hint # 5
Press for hint # 6
Press for hint # 7
Cl
MgCl
OH
OH