Option C, Solar Energy, Biofuel and Electron Conjugation
1. Photosynthesis convert light energy to chemical energy
Photosynthesis
Light absorb by chlorophyll/pigment/carotene
with conjugated electronic structure
Chlorophyll
Carotene
Light absorbingpigmentin chloroplast/leaves
Visible
light
Green
transmitted
absorbed
Chlorophyll
Electronexcited by photon
Redox rxn to produce ATP/NADPH
to reduce CO2 to glucose
Chlorophyllpigment
↓
Extensiveconjugationstructure
↓
Absorbin red/blueregion
↓
Green
electron excited
by photon
Absorb photon (visible region )- excited electron pass through ETC
(sequence redox rxn to drive ATP production) and reduce CO2 to glucose.
2. Photosynthesis convert light energy to chemical energy
Photosynthesis
Light absorb by chlorophyll/pigment/carotene
with conjugated electronic structure
Chlorophyll
Carotene
Light absorbingpigmentin chloroplast/leaves
Absorb photon (visible region )- excited electron pass through ETC
(sequence redox rxn to drive ATP production) and reduce CO2 to glucose.
Electronexcited by photon
Redox rxn to produce ATP/NADPH
to reduce CO2 to glucose
Two half eqn
Eqn photosynthesis
Photolysis water
(Oxidation)
CO2 reduction
(Reduction)
6CO2 + 24H+ + 24e- → C6H12O6 + 6 H2O12H2O → 6O2 + 24H+ + 24e-
6CO2 + 6 H2O → C6H12O6 + 6O2
electron excited
by photon
3. Triglyceride
Energy for vegetable oil
Too viscous
Ester of fatty acid and glycerol Through biological process,agricultureand anaerobic digestion
Biofuelmadefrom sugar, starch, or vegetable oil
Fermentation – using sugar/corn/cane produce ethanol
Biogas breakdown
organic matter by
anaerobic bacteria
Energy
Advantage
Renewable
Higheroctane rating
Ethanol,methane – biofuel
Biofuel
Bioethanol
C6H12O6 → C2H5OH+ 2CO2
Biogas
C6H12O6 → 3CH4 + 3CO2
Biodiesel
Methane
Biogas - methane
Disadvantage
Biomassused for fuel not for food
Use fertilizers, greenhousegas produced
Lower specific energythan fossil fuel
Transesterification – with ethanol/methanol– produce oil less viscous
Strong acid/base add
Reversible – smaller molecules – don’t pack – ethyl/methyl ester
Methanol
Ethanol
Ethyl ester
Methyl ester
VS
H+/OH-
Shorterchain – less viscous
4. Advantages and disadvantage of biodiesel/biofuel
Biomassused for fuel not for food
Use fertilizers,greenhouse gas produced
Lower specific energythan fossil fuel
More viscous than diesel
Advantage Disadvantage
Renewable
Carbon neutral/lowcarbon footprint
Biodegradable/non toxic
Higherflash pt/less flammable
Higheroctane rating
Ethanol,methane – biofuel
Deduce equation
Pentyloctanoate with methanol in presence catalyst
Transesterification
Produce less viscous ester
Pentyl gp replace by methyl gp
C7H15COOC5H11 + CH3OH → C7H15COOCH3 + C5H11OH
Pentyl gp Methyl gp
State eqn for complete combustion ethanol
Enthalpy combustion ethanol is 1367kJ mol-1
Find specific energy in kJ g-1
Compare octane and explain diff
C2H5OH + 3O2 → 3H2O + 2CO2
1mol – 1367kJ
RMM ethanol = 46.08
46.08 g – 1367 kJ
1g - (1367/46.08) kJ
= 29.67kJ g -1
2C8H18 + 25O2 → 8H2O + 16CO2
114.26 g – 5470 kJ
1g - (5470/114.26) kJ
1mol – 5470kJ
RMM octane = 114.26
= 47.87 kJ g -1
Less energyfrom ethanol
Ethanolpartiallyoxidized with OH gps attached
Energy Released
Ethanol < Octane
State two form biomass which can be convert to energy
Why biomass is likely to be impt fuel for future
When biomass decompose in absence O2 , name the gas released
Production of biogas, bioethanol/ biodiesel/fermentation
Fossil fuel non renewable. Biomass is renewable source.
Methane gas
5. C C
Absorption of UV by organic molecule and chromophores
Absorption UV radiation by
C = C, C = O, N = N, N =O gps
C = C /N = N (π bond)
C = O: (lone pair electron)
NO2 (lone pair electron)
Chromophores gp
Ground
Higheremptyorbital
π electron
AbsorbUV to excite π/lone pair e to higheremptyorbital
C O
lone pair
electron
:
Chromophores – organic molecule with conjugated double bond
Absorb radiation to excite delocalized e to empty orbital
alternating double/single bond
Filled orbital Bondingorbital
empty orbital antibonding orbital
Biological Pigments (Anthocyanins)
Coloured – extensive conjugation of electrons
alternating single and double bond
Porphyrin Chlorophyll Heme (hemoglobin)
Anthocyanin
Carotene
absorb absorb absorb absorb
6. C C
Absorption UV radiation by
C = C, C = O, N = N, N =O gps
C = C /N = N (π bond)
C = O: (lone pair electron)
NO2 (lone pair electron)
Ground
π electron
Absorb UV to excite π/lone pair e to higheremptyorbital
C O
lone pair
electron
:
alternating double/single bond
Carotene
Diff bet UV and Visible absorption
Colourless- Absorption in UV range
Electronic transitionfrom bonding to antibonding orbital
(involve pi / lone pair e)
UV visible
Organic molecules/chromophores
BiologicalPigments(Anthocyanins)
Coloured – extensive conjugationofelectron
Alternatingsingle and double bond
Electron in pi orbitaldelocalized through single and double bond.
π elec excitedby absorbinglongwavelengthin visible region
Anthocyanin
Chlorophyll
absorb absorb
Higheremptyorbital
Chromophore λ max/nm
C = C 175
C = O 190
C = C – C = C 210
- NO2 270
190- 260
Benzene ring – conjugatedsystem
7. Absorb radiation to excite delocalized e to empty orbital
Filled orbital
empty orbital
Carotene
Colourless – Absorption in UV range
Electronic transition frombondingto antibondingorbital
(involve pi / lonepair e)
UV visible
Anthocyanin
Absorption of UV/vis by organic molecule and pigment
Less conjugatedsystem
↓
Less alternating single/double bond
↓
Absorbshorter wavelength (UV)
↓
Colourless compound
More conjugated system
↓
More alternatingsingle/double bond
↓
Absorblonger wavelength (visible)
↓
Colour compound
alternating double/single bond
More conjugation → More delocalization → Absorption in visible range
Extensive conjugation of double bond allow more delocalization of π elec
More conjugation → More delocalization → Less energy to excite electron → ↓ E lower ( absorb at visible region (colour )
How number of conjugation led to colour formation from UV to visible?
BiologicalPigments(Anthocyanins)
Coloured – extensiveconjugation ofelectron
Alternatingsingle and double bond
Electron in pi orbitaldelocalized through single and double bond.
π elec excitedby absorbing long wavelength in visible region
8. UV visible
Absorption of UV/vis by organic molecule and pigment
More conjugation → More delocalization → Absorption in visible range
Extensive conjugation of double bond allow more delocalization of π electron
More conjugation → More delocalization → Less energy to excite electron → ↓ E lower ( absorb visible region (colour )
How number of conjugation led to colour formation from UV to visible?
More conjugation – splittingenergy less ∆E ↓ – wavelengthincrease (visible range)
Filled orbital
empty orbital
100 200 300 400 700nmWavelength λ
C – C C = C C = C – C = C C = C – C = C – C = C
∆E ↓with more conjugation
absorb from UV to visible
∆E ↓with more conjugation
Absorb at ↓ lower energy (↑ longer λ)
AbsorbUV – sunblock Absorb visible region – food dye (Azo dye)Acid/baseindicator
9. alternating double/single bond
CaroteneAnthocyanin Chlorophyll Heme (hemoglobin)
Wavelength - absorbed
Visible
light
Colour seen RED – RED reflect to eyes
- Blue absorb (complementary colour)
absorbed
RED
transmitted
Carotenoidsabsorb λ at 460 nm
Colour – extensiveconjugation ofelec.Alternatingsingle/doublebond
π elec delocalizedthrough single/double bond.
π elec excitedby absorbinglongwavelength in visible region
700 600 500 400
Biological Pigment
10. alternating double/single bond
CaroteneAnthocyanin Chlorophyll Heme (hemoglobin)
Wavelength - absorbed
Visible
light
Colour seen GREEN– GREEN reflect to eyes
- Red/Blue absorb (complementary colour)
absorbed
Green
transmitted
Chlorophyll absorb λ at 400 and 700nm
Colour – extensiveconjugation ofelec.Alternatingsingle/doublebond
π elec delocalizedthrough single/double bond.
π elec excitedby absorbinglongwavelength in visible region
700 600 500 400
Biological Pigment
11. C6H5–(CH=CH)6–C6H5
↓
More conjugate
↓
Absorb blue
↓
Complement colour reflect Orange
C6H5–(CH=CH)5–C6H5
↓
Less conjugate
↓
Absorbpurple
↓
Complement colour reflect Yellow
Anthocyanins – used as acid/baseindicator
Identify λ max which correspondto max absorbanceat diff pH
and suggest colour in acid/basecondition.
pH Max Colour absorb Colour pigment
1 550 Green Red
12 475 Blue Yellow/orange
wavelength wavelength
Anthocyanins – used as acid/base indicator
Identify λ max which correspond to max absorbanceat diff pH
and suggest colour in acid/base condition.
pH Max Colour absorb Colour pigment
1 550 Green Red
7 350 None visible Colourless
Describe relationship bet n and λ max
Suggest which series absorb in visible region
Suggest colour of C6H5–(CH=CH)5–C6H5 andC6H5–(CH=CH)6–C6H5
Increasen or conjugation → Absorption to longerwavelength λmax increase
Absorption from 400 – 700nm ( visible region) when n > 4
n = 5 n = 6
12. Tetracene - Greater delocalization elec (Higher conjugation bond)
- Absorb longer wavelength – visible light (colour)
Organic compoundsshown anthracene and tetracene.
Predict with reference to conjugation double bond,which absorbvisible light (colour)
Carotene absorb light in blue/green region, so complementary
colour (red and orange) are transmitted
Anthracene Tetracene
Absorptionspectrum ofcarotenewas shown. Explainwhy carotenehave colour.
Carotene
700 600 500 400
RED
Absorption spectrum of anthrocyaninis shown.
Explainwhat effect,the absorptionat 375 and 530 nm have on colour of anthrocyanin
At 375 nm - No effect, lies outside visible spectrum (UV region)
At 530 nm - Visible colour, red, complementary to blue-green
- Absorb green – Reflect Red
700 600 500 400 300 200
Anthocyanin
RED
13. CaroteneAnthocyanin Chlorophyll Heme (hemoglobin)
Wavelength - absorbed
Colour seen RED – RED reflect to eye
- Blue absorb
Anthrocyanin – acid base indicator
- absorb λ 550nm at pH 1 (acid)
Colour seen Yellow – yellow reflect to eye
- Blue absorb
Wavelength - absorbed
Anthrocyanin– acid base indicator
- absorb λ 470nm at pH 12 (alkali)
+ H+
+ OH-
Add acid
Add base
Change in numberOH gp
Changein numberconjugation
Absorbat diff wavelength
RED YELLOW
Numberconjugation increase
↓
Absorblonger wavelength
Numberconjugation decrease
↓
Absorbshorter wavelength
Colour – extensiveconjugation ofelec.Alternatingsingle/double bond
π elec delocalizedthroughsingle/doublebond.
π elec excitedby absorbinglongwavelength in visible region
Biological Pigment