Option C, Solar Energy, Biofuel and Electron Conjugation

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Prepared by Lawrence Kok

Option C Solar Energy, Electron Conjugation and Biodiesel

http://lawrencekok.blogspot.com/

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:


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


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


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




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



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



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


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)



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

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucnot.html

http://www.m2c3.com/chemistry/VLI/M3_Topic2/M3_Topic2_print.html

Option C, Solar Energy, Biofuel and Electron Conjugation

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Transcript of Option C, Solar Energy, Biofuel and Electron Conjugation