ib chemistry resonance, delocalization for ozone and benzene
DESCRIPTION
IB Chemistry Resonance, Delocalization for Ozone and BenzeneTRANSCRIPT
Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
bull All bonds O-O are identical in length and strengthbull Hybrid of 2 resonance structuresbull NO O-O (single) or O=O (double) bonds foundbull Only O ----- O bondbull Intermediate in character bet single and double bond
bull Bond Order = 211
Ozone3O
Click here on video ozone
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
bull Pale blue gas polar dimagneticbull Oxidizing agentbull Potent respiratory hazard and pollutant at ground levelbull Beneficial prevent UV BC from reaching Earth surfacebull Highest ozone level in stratosphere (10 km and 50 km)
UV radiation
Ozone at stratosphere
strongest radiation
3O
FORMAL CHARGE (FC)
Formal Chargebull ToolModel for comparing which Lewis structures is more acceptablebull Treats covalent bond with equal electron distribution no electronegativity differences bet atombull Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom
L ndash lone pair electron
B ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion 0
+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bull Pollutant bull Photochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer- DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double
bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV lt242nm lt330nm
Ozone weaker bondbull Absorb UV AB(wavelength 330nm)
Bonding
O2 and O3
Oxygen stronger bondbull Absorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone protect
Oxygen split by
high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
FORMAL CHARGE (FC)
Formal Chargebull ToolModel for comparing which Lewis structures is more acceptablebull Treats covalent bond with equal electron distribution no electronegativity differences bet atombull Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V - valence electrons of atom
L ndash lone pair electron
B ndash bonding electron molecule
Formal charge sulfur dioxide
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 ndash (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 ndash (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6
FC = 6 ndash (2+3) = +1
All resonance structure contribute to electronic structure Real structure is combination of themLowest formal charge (stable) contribute more than less stable structureSum of formal charges must be zero for neutral or equal to charge on ion 0
+1
-1
L + L + L +
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bull Pollutant bull Photochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer- DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double
bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV lt242nm lt330nm
Ozone weaker bondbull Absorb UV AB(wavelength 330nm)
Bonding
O2 and O3
Oxygen stronger bondbull Absorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone protect
Oxygen split by
high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Ozone Good and Bad Good Side Bad Side
Ozone in Strastopherebull blocks UV B + C
Ozone in Troposphere act asbull Greenhouse gas
Ozone in ground level act as bull Pollutant bull Photochemical
Click here on ozone depletion substances ODS (phaseout)
Why ozone able to absorb UV B and UV C
Breakdown of ozone ndash High UV radiation ndash Skin cancer- DNA mutation
Ozone depletion
UV Exposure
Ozone Hole
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double
bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV lt242nm lt330nm
Ozone weaker bondbull Absorb UV AB(wavelength 330nm)
Bonding
O2 and O3
Oxygen stronger bondbull Absorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone protect
Oxygen split by
high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Ozone absorb UV radiation
Ozone absorb UV BC
Ozone formation
O=O Double
bond
O=O=OInter
mediate
Bond lengthpm 121 127
Bond enthalpykJ mol-1
498 364
Bond order 2 15
Dissociation by UV lt242nm lt330nm
Ozone weaker bondbull Absorb UV AB(wavelength 330nm)
Bonding
O2 and O3
Oxygen stronger bondbull Absorb UV C (wavelength 230nm)
Free radical -reactive species with unpair electron
How ozone layer protect life on earth
Ozone Cycle
How Ozone protect
Oxygen split by
high UV to O (radical)
O radical combine to form ozone
1
2
3 Ozone (stratosphere) absorb UV BC
4Ozone reform again
Ozone cycle
Ozone createddestroyed by Chapman cycle
Oxygen reform again
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Ozone absorb UV BC
CFC breaks down
How CFC breaks down
High UV BC
How CI radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
How CFC destroys ozone
CI free radicals form
CImiddot react O3 form CIOmiddot radical
CIOmiddot react Omiddot form CImiddot radical again
Net eqn- ozone break down
Carbon
Fluorine
Chlorine
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
+
Ozone absorb UV BC
NOx breaks down
How CFC breaks down
High UV BC
How NO radical destroy ozone
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
NO free radicals form
NO react O3 form NO2 radical
NO2 react O form NO radical again
Net eqn- ozone breaks down
Oxides of Nitrogen
Nitrogen Dioxide
(NO2)
Nitrogen monoxide
(nitric oxide NO)
Nitrous oxide
N2O
Break down to form NO free radical (unpair electron)
NO NO2
NO2 NO + O2
Sources of NOx
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Catalytic destruction of ozone
Ozone Depleting Substances (ODS)
Source of ODSbullHalogenated substancebullMan-made halocarbon refrigerant solvent propellantbullFoam-blowing agent (CFCs HCFCs freons halons)
Montreal Protocol bans CFC halon and ODS like carbon tetrachloride and trichloroethane
CFCbull Contain chlorine fluorine and carbon atomsbull Extremely stable with strong bonds long half lifebull Stability allows CFC into the stratosphere bull High UV radiation reacts with CFCbull High UV photons breaks CFC (photochemical
decomposition) bull Free Cl radicals form - destroying ozone
TrichloroflouromethaneCFC-11
Dichlorodifluoromethane CFC-12
ChlorodifluoromethaneHCFC-22
Why halogenated
CFC used
Less harmful
Very harmful
Why fluorinated is safer
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
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Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
Delocalization of electrons
Resonance bull Describing delocalization of electrons within a moleculepolyatomic ionwhere bonding cannot be express by ONE single Lewis structurebullDelocalization of π bond ndash π electrons spread over more than 2 nuclei
bullπ electrons are shared
bullπ electrons spread ndash more stable
Resonance structures benzene
Benzene6HC6
resonance structure 1 resonance structure 2
Resonance hybrid
bull All bonds C6H6 are identical in length strengthbull Hybrid of 2 resonance structuresbull No C-C (single) or C=C (double) bonds foundbull Only C ----- C bondbull Intermediate character bet singledouble bond
bull Bond Order =
bull Unhybridised p orbitalbull Delocalization electrons above below planebull sp2 hybridization on carbon center
15
Click here to view
Delocalized electrons
Kekuleacute structure
Cyclohexa- 135 triene
χ doublesingle bonds bet them
Benzene
Hexagonal planar
Resonance Hybrid more stable than any of the resonance structure
Click here to view
Kekule
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond
ResonanceDelocalization Energy
ΔH cyclohexene = -120kJmol-1
ΔH cyclohexa 13 diene = -240kJmol-1
ΔH cyclohexa 135 triene = -360kJmol-1
ΔH Benzene = -208kJmol-1
Enthalpy change hydrogenation
χ
helliphellip
bull Benzene lower in energy by 150kJbull More stable due to delocalization
of π electrons
150kJ
-150
C-CSingle bond
C=CDouble bond
C=CBenzene
Bond lengthpm 154 134 140
Bond enthalpykJmol-1
346 614 507
3 Evidence for Benzene structure1
2
Click here evidence against Kekule
bull X ray hit benzene crystalbull Interact with electron (electron density map) bull X ray diffraction producedbull Bond length measured
X ray crystallography
NO singledouble bond detected
3 Addition reaction for unsaturated C=C
Addition reaction
Substitution reaction
NO double bond