option c, solar energy, biofuel and electron conjugation

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

Green

transmitted

absorbed

Chlorophyll

Electron excited by photon Redox rxn to produce ATP/NADPH to 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 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 H2O 12H2O → 6O2 + 24H+ + 24e-

6CO2 + 6 H2O → C6H12O6 + 6O2

electron excited by photon

Triglyceride Energy for vegetable oil Too viscous Ester of fatty acid and glycerol Through biological process, agriculture and anaerobic digestion

Biofuel made from sugar, starch, or vegetable oil Fermentation – using sugar/corn/cane produce ethanol

Biogas breakdown organic matter by anaerobic bacteria

Energy

Advantage Renewable

Higher octane rating Ethanol, methane – biofuel

Biofuel

Bioethanol

C6H12O6 → C2H5OH+ 2CO2

Biogas

C6H12O6 → 3CH4 + 3CO2

Biodiesel

Methane

Biogas - methane

Disadvantage Biomass used for fuel not for food

Use fertilizers , greenhouse gas produced Lower specific energy than 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-

Shorter chain – less viscous

Advantages and disadvantage of biodiesel/biofuel

Biomass used for fuel not for food Use fertilizers, greenhouse gas produced

Lower specific energy than fossil fuel More viscous than diesel

Advantage Disadvantage

Renewable Carbon neutral/low carbon footprint

Biodegradable/non toxic Higher flash pt/less flammable

Higher octane 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 energy from ethanol Ethanol partially oxidized 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

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

Absorb 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 range Electronic 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 absorb

Higher empty orbital

Chromophore λ max/nm

C = C 175

C = O 190

C = C – C = C 210

- NO2 270

190- 260

Benzene 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 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?

Biological Pigments (Anthocyanins) Coloured – extensive conjugation of electron

Alternating single and double bond Electron in pi orbital delocalized through single and double bond.


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 – 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 conjugation absorb from UV to visible

∆E ↓with more conjugation Absorb at ↓ lower energy (↑ longer λ)

Absorb UV – sunblock Absorb visible region – food dye (Azo dye) Acid/base indicator


Carotene Anthocyanin Chlorophyll Heme (hemoglobin)

Wavelength - absorbed

Visible light

Colour seen RED – RED reflect to eyes - Blue absorb (complementary colour)

absorbed

RED

transmitted

Carotenoids absorb λ at 460 nm

Colour – extensive conjugation of elec. Alternating single/double bond π elec delocalized through single/ double bond.


700 600 500 400

Biological Pigment




Visible light

Colour seen GREEN– GREEN reflect to eyes - Red/Blue absorb (complementary colour)

absorbed

Green

transmitted

Chlorophyll absorb λ at 400 and 700nm



700 600 500 400

Biological Pigment

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 indicator Identify 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 indicator Identify 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 region Suggest colour of C6H5–(CH=CH)5–C6H5 and C6H5–(CH=CH)6–C6H5

Increase n or conjugation → Absorption to longer wavelength λmax increase Absorption 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

Anthocyanin RED



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 gp Change in number conjugation Absorb at diff wavelength

RED YELLOW

Number conjugation increase ↓

Absorb longer wavelength

Number conjugation decrease ↓

Absorb shorter wavelength



Biological Pigment

option c, solar energy, biofuel and electron conjugation

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