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Prepared by Lawrence Kok
Option C Solar Energy, Electron Conjugation and Biodiesel
Photosynthesis convert light energy to chemical energy
Photosynthesis
Light absorb by chlorophyll/pigment/carotene with conjugated electronic structure
Chlorophyll
Carotene
Light absorbing pigment in chloroplast/leaves
Visible light
Greentransmitted
absorbed
Chlorophyll
Electron excited by photonRedox rxn to produce ATP/NADPHto reduce CO2 to glucose
Chlorophyll pigment ↓
Extensive conjugation structure↓
Absorb in red/blue region↓
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.
Photosynthesis convert light energy to chemical energy
Photosynthesis
Light absorb by chlorophyll/pigment/carotene with conjugated electronic structure
Chlorophyll
Carotene
Light absorbing pigment in chloroplast/leaves
Absorb photon (visible region )- excited electron pass through ETC (sequence redox rxn to drive ATP production) and reduce CO2 to glucose.
Electron excited by photonRedox rxn to produce ATP/NADPHto 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
TriglycerideEnergy for vegetable oilToo viscousEster of fatty acid and glycerol Through biological process, agriculture and anaerobic
digestionBiofuel made from sugar, starch, or vegetable oil
Fermentation – using sugar/corn/cane produce ethanol
Biogas breakdown organic matter byanaerobic bacteria
Energy
AdvantageRenewable
Higher octane ratingEthanol, methane – biofuel
Biofuel
Bioethanol
C6H12O6 → C2H5OH+ 2CO2
Biogas
C6H12O6 → 3CH4 + 3CO2
Biodiesel
Methane
Biogas - methaneDisadvantage
Biomass used for fuel not for foodUse fertilizers , greenhouse gas produced
Lower specific energy than fossil fuel
Transesterification – with ethanol/methanol– produce oil less viscousStrong acid/base addReversible – smaller molecules – don’t pack – ethyl/methyl ester
Methanol
Ethanol
Ethyl ester
Methyl ester
VS
H+/OH-
Shorter chain – less viscous
Advantages and disadvantage of biodiesel/biofuel
Biomass used for fuel not for foodUse fertilizers, greenhouse gas produced
Lower specific energy than fossil fuelMore viscous than diesel
Advantage Disadvantage
RenewableCarbon neutral/low carbon footprint
Biodegradable/non toxicHigher flash pt/less flammable
Higher octane ratingEthanol, methane – biofuel
Deduce equation Pentyloctanoate with methanol in presence catalyst
TransesterificationProduce 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 diffC2H5OH + 3O2 → 3H2O + 2CO2
1mol – 1367kJRMM 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 – 5470kJRMM octane = 114.26
= 47.87 kJ g -1
Less energy from ethanolEthanol partially oxidized with OH gps attached
Energy ReleasedEthanol < Octane
State two form biomass which can be convert to energyWhy biomass is likely to be impt fuel for future
When biomass decompose in absence O2 , name the gas released
Production of biogas, bioethanol/ biodiesel/fermentationFossil fuel non renewable. Biomass is renewable source.Methane gas
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
Higher empty orbital
π electron
Absorb UV to excite π/lone pair e to higher empty orbital
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 Bonding orbital
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
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
Absorpb UV to excite π/lone pair e to higher empty orbital
C O lone pair electron:
alternating double/single bond
Carotene
Diff bet UV and Visible absorption
Colourless - Absorption in UV rangeElectronic transition from bonding to antibonding
orbital (involve pi / lone pair e)
UV visible
Organic molecules/chromophores
Biological Pigments (Anthocyanins)Coloured – extensive conjugation of electron
Alternating single and double bond Electron in pi orbital delocalized through single and
double bond. π elec excited by absorbing long wavelength in visible
region
Anthocyanin
Chlorophyll
absorb absorbHigher empty orbital
Chromophore λ max/nm
C = C 175
C = O 190
C = C – C = C 210
- NO2 270
190- 260Benzene ring – conjugated system
Absorb radiation to excite delocalized e to empty orbital
Filled orbital
empty orbital
Carotene
Colourless – Absorption in UV range Electronic transition from bonding to antibonding
orbital (involve pi / lone pair e)
UV visible
Anthocyanin
Absorption of UV/vis by organic molecule and pigment
Less conjugated system↓
Less alternating single/double bond↓
Absorb shorter wavelength (UV)↓
Colourless compound
More conjugated system↓
More alternating single/double bond↓
Absorb longer wavelength (visible)↓
Colour compound
alternating double/single bond
More conjugation → More delocalization → Absorption in visible rangeExtensive conjugation of double bond allow more delocalization of π elecMore 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?
Biological Pigments (Anthocyanins)Coloured – extensive conjugation of electron
Alternating single and double bond Electron in pi orbital delocalized through single and
double bond. π elec excited by absorbing long wavelength in visible
region
UV visible
Absorption of UV/vis by organic molecule and pigments
More conjugation → More delocalization → Absorption in visible rangeExtensive conjugation of double bond allow more delocalization of π electronMore 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 – splitting energy less ∆E ↓ – wavelength increase (visible range)
Filled orbital
empty orbital
100 200 300 400 700nm Wavelength λ
C – C C = C C = C – C = C C = C – C = C – C = C
∆E ↓with more conjugationabsorb from UV to visible
∆E ↓with more conjugationAbsorb at ↓ lower energy (↑ longer λ)
Absorb UV – sunblock Absorb visible region – food dye (Azo dye)Acid/base indicator
alternating double/single bond
CaroteneAnthocyanin Chlorophyll Heme (hemoglobin)
Wavelength - absorbed
Visible light
Colour seen RED – RED reflect to eyes - Blue absorb (complementary colour)
absorbed
REDtransmitted
Carotenoids absorb λ at 460 nm
Colour – extensive conjugation of elec. Alternating single/double bond
π elec delocalized through single/ double bond. π elec excited by absorbing long wavelength in visible
region
700 600 500 400
Biological Pigment
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
Greentransmitted
Chlorophyll absorb λ at 400 and 700nm
Biological Pigment
Colour – extensive conjugation of elec. Alternating single/double bond
π elec delocalized through single/ double bond. π elec excited by absorbing long wavelength in visible
region
700 600 500 400
C6H5–(CH=CH)6–C6H5
↓More conjugate
↓Absorb blue
↓Complement colour reflect
Orange
C6H5–(CH=CH)5–C6H5
↓Less conjugate
↓Absorb purple
↓Complement colour reflect
Yellow
Anthocyanins – used as acid/base indicatorIdentify λ max which correspond to max absorbance at
diff pH and suggest colour in acid/base condition.
pH Max Colour absorb
Colour pigment
1 550 Green Red
12 475 Blue Yellow/orange
wavelength wavelength
Anthocyanins – used as acid/base indicatorIdentify λ max which correspond to max absorbance at
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 regionSuggest colour of C6H5–(CH=CH)5–C6H5 and C6H5–
(CH=CH)6–C6H5 Increase n or conjugation → Absorption to longer wavelength λmax increaseAbsorption from 400 – 700nm ( visible region) when n > 4
n = 5 n = 6
Tetracene - Greater delocalization elec (Higher conjugation bond) - Absorb longer wavelength – visible light (colour)
Organic compounds shown anthracene and tetracene.Predict with reference to conjugation double bond, which absorb visible light (colour)
Carotene absorb light in blue/green region, so complementary colour (red and orange) are transmitted
Anthracene Tetracene
Absorption spectrum of carotene was shown. Explain why carotene have colour.
Carotene
700 600 500 400
RED
Absorption spectrum of anthrocyanin is shown.Explain what effect, the absorption at 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
AnthocyaninRED
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 number OH gpChange in number conjugationAbsorb at diff wavelength
RED YELLOW
Number conjugation increase ↓
Absorb longer wavelength
Number conjugation decrease ↓Absorb shorter wavelength
Biological Pigments (Anthocyanins)
Colour – extensive conjugation of elec. Alternating single/double bond
π elec delocalized through single/ double bond. π elec excited by absorbing long wavelength in visible
region
Acknowledgements
Thanks to source of pictures and video used in this presentationhttp://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucnot.htmlhttp://www.m2c3.com/chemistry/VLI/M3_Topic2/M3_Topic2_print.htmlhttp://www.universityneurosurgery.com/index.php?srchttp://www.medwow.com/med/cobalt-linear-accelerator/radon/tr-cobalt-60/42865.model-spechttp://endocrinesurgery.ucla.edu/patient_education_adm_tst_radioactive_iodine_uptake_test.html
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/
Prepared by Lawrence Kok
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