option c, solar energy, biofuel and electron conjugation
TRANSCRIPT
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 :
alternating double/single bond
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
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?
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 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
alternating double/single bond
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.
π elec excited by absorbing long wavelength in visible region
700 600 500 400
Biological Pigment
alternating double/single bond
Carotene Anthocyanin 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 – 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
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
Carotene Anthocyanin 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 gp Change in number conjugation Absorb at diff wavelength
RED YELLOW
Number conjugation increase ↓
Absorb longer wavelength
Number conjugation decrease ↓
Absorb shorter wavelength
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
Biological Pigment