Class Functional gp Suffix Example Formula Alkane C - C - ane ethane C n H 2n+2 H H ׀ ׀H - C – C – H ׀ ׀H H H ׀H - C – H ׀H H H H ׀ ׀ ׀H - C – C – C – H ׀ ׀ ׀H H H H H H H ׀ ׀ ׀ ׀H - C – C – C – C – H ׀ ׀ ׀ ׀H H H H Number carbon Word IUPAC name Structure formula Molecular formula 1 Meth Methane CH 4 CH 4 2 Eth Ethane CH 3 CH 3 C 2 H 6 3 Prop Propane CH 3 CH 2 CH 3 C 3 H 8 4 But Butane CH 3 (CH 2 ) 2 CH 3 C 4 H 10 5 Pent Pentane CH 3 (CH 2 ) 3 CH 3 C 5 H 12 6 Hex Hexane CH 3 (CH 2 ) 4 CH 3 C 6 H 14 7 Hept Heptane CH 3 (CH 2 ) 5 CH 3 C 7 H 16 8 Oct Octane CH 3 (CH 2 ) 6 CH 3 C 8 H 18 9 Non Nonane CH 3 (CH 2 ) 7 CH 3 C 9 H 20 10 Dec Decane CH 3 (CH 2 ) 8 CH 3 C 10 H 22 methane ethane propane butane Saturated hydrocarbon (C – C single bond) Chemical rxn Alkane Reactivity for Alkanes Combustion rxn Complete combustion – produce CO 2 + H 2 O • C 2 H 6 + 7/2O 2 → 2CO 2 + 3H 2 O Incomplete combustion – produce C, CO, CO 2 , H 2 O • 2C 3 H 8 + 7O 2 → 2C + 2CO + 8H 2 O + 2CO 2 Free Radical Substitution rxn Free Radical Substitution Mechanism - Homolytic fission- bond break by radical form. - Covalent bond split, each atom obtain one electron (unpair e) - UV needed - Radical react with molecule - Radical + radical → molecule CH 4 + CI 2 → CH 3 CI + HCI • Low reactivity - Strong stable bond bet C - C, C - H • Low reactivity - Low polarity of C - H bond • Saturated hydrocarbon – Non polar bond Initiation Propagation Radical (dot) Termination homolytic fission Radical recycle again 1 2
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IB Chemistry Nucleophilic Substitution, SN1, SN2 and protic solvent
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Reactivity for halogenoalkane • Carbon bond to halogen – F, CI, Br, I • High electronegativity on halogen gp • High reactivity – due to polarity of C+- Br -
Nucleophile – Lone pair electron – Donate electron pair (Lewis base)
Chemical rxn Halogenoalkane
C - Br ᵟ+ ᵟ-
electron
Electron deficient
carbon
O–H ..
..
ᵟ- ᵟ+
C ᵟ+
Substitution rxn
CH3CH2CI + OH- → CH3CH2OH + CI-
H H
׀ ׀
H - C – C – CI
׀ ׀
H H
+ OH- ᵟ+ ᵟ-
H H
׀ ׀
H - C – C – OH + CI-
׀ ׀
H H
H Br H
׀ ׀ ׀
H - C – C – C – H
׀ ׀ ׀
H H H
CH3CHBrCH3 + OH- → CH3CHOHCH3 + Br-
+ OH-
H OH H
׀ ׀ ׀
H - C – C – C – H + Br-
׀ ׀ ׀
H H H
ᵟ+
ᵟ-
CH3 H
׀ ׀
CH3 – C – C – CI
׀ ׀
CH3 H
Electrophile - Electron deficient - Accept lone pair - Positive charge - Lewis Acid
C - Br
Reactivity for halogenoalkane • Carbon bond to halogen – F, CI, Br, I • High electronegativity on halogen gp • High reactivity – due to polarity of C+- CI -
C - Br ᵟ+ ᵟ-
electron
Electron deficient carbon
OH ..
ᵟ- ᵟ+
Nucleophilic Substitution rxn
CH3CH2CI + OH- → CH3CH2OH + CI-
H H
׀ ׀
H - C – C – CI
׀ ׀
H H
+ OH- ᵟ+ ᵟ-
H H
׀ ׀
H - C – C – OH + CI-
׀ ׀
H H
H Br H
׀ ׀ ׀
H - C – C – C – H
׀ ׀ ׀
H H H
CH3CHBrCH3 + OH- → CH3CHOHCH3 + Br-
+ OH-
H OH H
׀ ׀ ׀
H - C – C – C – H + Br-
׀ ׀ ׀
H H H
ᵟ+ ᵟ-
Nucleophile and Substitution Electrophile and Addition
vs Reactivity of Alkene - High reactivity - Unstable bond bet C = C - High reactivity – Weak pi bond overlap bet p orbital - Unsaturated hydrocarbon – ᴨ bond overlap
C = C Electron rich π electron
ᵟ- ᵟ-
H ᵟ+
C = C ᵟ- ᵟ-
E ᵟ+
E+ Electron deficient Nu
ᵟ-
ᵟ-
Nucleophile – Lone pair electron – Donate electron pair - Lewis Base
H H ׀ ׀
C = C
׀ ׀ H H
CH2=CH2 + Br2 → CH2BrCH2Br
+ Br – Br ᵟ- ᵟ+
H H ׀ ׀
H - C – C – H
׀ ׀ Br Br
vs
CH2=CH2 + HCI → CH3CH2CI
H H ׀ ׀
C = C
׀ ׀ H H
ᵟ- + H – CI
ᵟ+
H H ׀ ׀
H - C – C – H
׀ ׀ H CI
Electrophilic Addition rxn
Electrophile - Electron deficient - Accept lone pair - Positive charge - Lewis Acid
ᵟ-
Electron rich region
Electrophilic Substitution rxn
C6H6 + Br2 C6H5Br + HBr
+ Br-Br ᵟ+
+ NO2+
ᵟ+
Electrophile and Substitution Electrophile and Addition
vs
C = C Electron rich π electron
ᵟ- ᵟ-
ᵟ+
C = C ᵟ- ᵟ-
E ᵟ+
E+ Electron deficient
E ᵟ+
H H ׀ ׀
C = C
׀ ׀ H H
CH2=CH2 + Br2 → CH2BrCH2Br
+ Br – Br ᵟ- ᵟ+
H H ׀ ׀
H - C – C – H
׀ ׀ Br Br
vs
CH2=CH2 + HCI → CH3CH2CI
H H ׀ ׀
C = C
׀ ׀ H H
ᵟ- + H – CI ᵟ+
H H ׀ ׀
H - C – C – H
׀ ׀ H CI
Electrophilic Addition rxn
E
Electrophile - Electron deficient - Accept lone pair - Positive charge - Lewis Acid
ᵟ+ + H E
+ H
Electron rich region
H Br
+ HBr
C6H6 + HNO3 C6H5NO2 + HCI
AICI3 dry ether
warm/Conc H2SO4
H NO2
Reactivity of Alkene - High reactivity - Unstable bond bet C = C - High reactivity – Weak pi bond overlap bet p orbital - Unsaturated hydrocarbon – ᴨ bond overlap
Reactivity of Benzene (Unreactive) - Delocalization of electron in ring - Stability due to delocalized π electron - Substitution instead of Addition
ethene decolourize brown Br2(I)
benzene –stable (unreactive) toward addition rxn
H
C6H6 – no rxn with brown Br2(I)
Electrophile - Electron deficient - Accept lone pair - Positive charge - Lewis Acid
C - Br OH .. ᵟ- ᵟ+
Nucleophile Electrophile
ᵟ+
C = C ᵟ-
Nucleophile – Lone pair electron – Donate electron pair - Lewis Base
Reactivity for halogenoalkane • Carbon bond to halogen – F, CI, Br, I • High electronegativity on halogen • High reactivity – polarity of C+- Br -
Nucleophile – Lone pair electron – Donate electron pair - (Lewis base)
Chemical rxn Halogenoalkane
C - Br ᵟ+ ᵟ-
electron
Electron deficient
carbon
O–H ..
.. ᵟ-
C ᵟ+
H H
׀ ׀
H - C – C – Br
׀ ׀
H H
+ OH- ᵟ+ ᵟ-
H H
׀ ׀
H - C – C – OH + Br-
׀ ׀
H H
Nucleophilic Substitution
Primary 10 - SN2
Primary 10 - SN2
- Experimentally rate expression = k [CH3CH2Br][OH-] - Rate dependent on conc- CH3CH2Br and OH-
- Molecularity = 2 - No bulky alkyl gp, less steric effect - Allow nucleophile to attack electron deficient carbon from opposite site (Inversion of configuration)
Bond Breaking and Making at transition state Br leaving gp substituted with OH-
H H
׀ ׀ CH3 - C – Br + OH- CH3 – C – OH + Br - ׀ ׀ H H
Nucleophile collide with bromoethane
CH3CH2Br + OH- → CH3CH2OH + Br- Single step
Nucleophilic Substitution
Click here view SN2
SN2 Substitution
Nucleophilic
Bimolecular Nucleophilic Substitution
Bimolecular collision bet 2 molecule
- Experimentally rate expression = k [CH3CH2Br][OH-] - Rate dependent on conc = CH3CH2Br and OH-
- Molecularity = 2 - No bulky alkyl gp, less steric effect - Allow nucleophile to attack electron deficient carbon from the opposite site (Inversion of configuration)
Nucleophile – Lone pair electron – Donate electron pair - (Lewis base)
CH3
׀
CH3 – C – Br
׀
CH3
CH3
׀
CH3 – C – Br
׀
CH3
R
׀
R – C – Br
׀
R
Reactivity for halogenoalkane • Carbon bond to halogen gp – F, CI, Br, I • High electronegativity on halogen gp • High reactivity – polarity of C+- Br -
Chemical rxn Halogenoalkane
C - Br ᵟ+ ᵟ-
electron
Electron deficient
carbon
O–H ..
.. ᵟ-
C ᵟ+
+ OH- ᵟ+ ᵟ-
Nucleophilic Substitution
Tertiary 30 – SN1
Tertiary 30 – SN1
- Experimentally rate expression = k [(CH3)3CBr] - Rate dependent on conc - (CH3)3CBr
- Molecularity = 1 - 3 Bulky alkyl gp, Steric hindrance effect - 30 carbocation more stable due to inductive effect • 3 alkyl gp stabilize carbocation by inductive effect push electron to carbocation (reducing positive charge) making it more stable
- 3 Bulky alkyl gp - Steric hindrance effect - 30 carbocation more stable due to inductive effect • 3 alkyl gp stabilize carbocation by inductive effect push electron to carbocation (reducing positive charge) making it more stable
- Experimentally rate expression = k [CH3CHBrCH3][OH-] - Rate dependent conc = CH3CHBrCH3 and OH-
- Molecularity = 2 - No bulky alkyl gp, less steric effect - Allow nucleophile to attack electron deficient carbon from opposite site (Inversion of configuration)
SN2 Substitution
Bimolecular collision bet 2 molecule
Nucleophilic
Bimolecular Nucleophilic Substitution
HO-
Bond breaking and making in transition state
+ Br-
One step mechanism – Bond break and making in transition state