Photosynthesis

• Organic Chemistry is the branch of chemistry that deals with carbon compounds
• The importance of Organic Chemistry lies in the vast number of organic compounds, their occurrences, and applications in daily life
• Carbon is unique due to its tetravalent nature, allowing it to form covalent bonds with other atoms
• Catenation is the ability of carbon to form stable chain-like structures by combining with other carbon atoms
• Carbon forms strong C-C covalent bonds and can also form multiple bonds, leading to a variety of carbon compounds
• Hybridization in carbon involves mixing of atomic orbitals to form new hybrid orbitals, such as sp3, sp2, and sp
• In sp3 hybridization, one s orbital mixes with 3 p orbitals to form 4 sp3 hybrid orbitals in a tetrahedral shape
• The sp3 hybrid orbitals in carbon are used in the formation of alkanes, which are saturated hydrocarbons
• Sp2 hybridization in carbon involves mixing one 2s orbital and two 2p orbitals to form three sp2 hybrid orbitals in a trigonal shape
• Sp2 hybrid orbitals in carbon are used in the formation of alkenes, which have a planar molecular structure
• Sp hybridization in carbon involves mixing one 2s orbital and one 2p orbital to form two sp hybrid orbitals in a linear shape
• Sp hybrid orbitals in carbon are used in the formation of alkynes, which have a triple bond between carbon atoms
• Ethyne has 3 bonds between the 2 carbon atoms, consisting of 1 σ and 2 π bonds
• The triple bond in ethyne makes it more reactive than ethene
• Alkynes, like ethyne, are more reactive than alkenes
• The C≡C bond in ethyne is shorter (1.2 Å) than the C=C bond (1.34 Å)
• sp hybridization is common to all alkynes
• Summary of sp hybridization:

  • Diagonal/linear shape
  • Bond angle of 180°
  • Formation of alkynes
• Electronegativity of hybridized orbitals:

  • The greater the s character of a hybrid orbital, the greater the electronegativity relative to other unhybridized bonding orbitals
  • Electronegativity scale: sp > sp2 > sp3
• Increasing the p character (or decreasing the s character) of the bond decreases the bond angle, and vice versa
• Determination of molecular composition and structure of organic compounds involves:

  1. Isolation and purification of the compound

  2. Qualitative analysis, including tests for elements and functional groups

  3. Quantitative analysis, including combustion experiments and determination of empirical and molecular formulas

  4. Structure determination, involving spectroscopic analysis, preparation of derivatives, degradation reactions, and synthesis
• Isolation and purification of organic compounds:

  • Can be isolated from natural sources like plants, soil, and microorganisms
  • Involves extraction with solvents of different polarities and chromatographic techniques like TLC, CC, PC, and HPLC
• Qualitative analysis of organic compounds:

  • Involves tests for elements and functional groups
  • Test for C and H is unnecessary as most organic compounds contain them
  • Presence of N, S, and Halogens detected by Lassaigne's test
• Test for Nitrogen:

  • Add FeSO4 solution to a portion of the filtrate
  • Heat, cool, add Fe(III) sulfate and dilute H2SO4
  • Blue or green coloration indicates the presence of CN (N)
• Test for Sulphur:

  • Add dilute HNO3 and lead ethanoate solution to a portion of the filtrate
  • Black precipitate of lead sulphide confirms presence of S
• Test for Halogens:

  • Heat with dil. HNO3 to remove N/S, cool, then add AgNO3
  • Different precipitates indicate presence of Cl-, Br-, or I-
• Quantitative analysis aims to determine the relative amount of elements in an organic compound

  • Determination of C and H involves burning the compound and calculating the weights of CO2 and H2O
• Calculation of Empirical Formula:

  • The ratio of the number of atoms of each element in the compound
  • Calculated from the percentage composition of elements
• For compound X:

  • Empirical Formula (E.F.) is CH2O
  • Molecular Formula (M.F.) is C4H8O4
  • Determination of Molecular Mass (MM) is essential to find the M.F.
  • Modern method for determining MM is High Resolution Mass Spectrometry (HRMS)
  • Once the M.F. is known, the structural formula of the compound can be determined
• For compound B:

  • Empirical Formula (E.F.) is CH2
  • Molecular Formula (M.F.) is C9H18
  • Combustion of compound B produced 8.36 mg of H2O and 20.47 mg of CO2
  • Quantitative analysis showed the absence of N, S, and halogens
• For compound D:

  • Empirical Formula (E.F.) is C3H6O2
  • Molecular Formula (M.F.) is C3H6O2
  • Quantitative analysis revealed 48.76% C, 8.07% H, and 43.17% O
  • No other elements were found in compound D
• Functional Group Classes of Organic Compounds:

  • Functional groups determine the chemical identity/reactions of a compound
  • Different functional groups constitute various homologous series
  • Homologous series have the same general formula and differ by a -CH2- unit
  • Alkanes are the simplest homologous series with the formula CnH2n+2
• Systematic Nomenclature:

  • The longest continuous chain containing the principal functional group is the parent chain
  • Carbon atoms in the chain are numbered to indicate the position of substituents/functional groups
  • Substituents are named in alphabetical order
  • Cyclic compounds are named with the prefix cyclo-
• In organic chemistry, when there are more than one substituent on the chain, the names of the substituents are written in alphabetical order
• For compounds with more than one functional group, the higher functional group is taken as the parent compound while the others are named as substituents
• The priority of functional groups in naming compounds is as follows:

  • Alkanes
  • Arenes
  • Nitro
  • Halo
  • Alkenes
  • Alkynes
  • Ethers
  • Amines
  • Alkanols
  • Alkanones (Ketones)
  • Alkanals (Aldehyde)
  • Alkanonitrile
  • Amides
  • Acidhalides
  • Esters
  • Carboxylic acids
  • Acid anhydride
• In writing the name of compounds, the names are written as one word, with numbers separated by commas and from substituent names by hyphens
• Chemical kinetics is the study of how fast chemical reactions occur, measured by the change in concentration of reactants or products with time
• Chemical reactions can be classified into three types based on speed:

  • Instantaneous reactions (e.g., ionic reactions)
  • Moderate reactions (e.g., hydrolysis of esters)
  • Very slow reactions (e.g., rusting of iron)
• Factors affecting reaction rate include temperature, concentration of reactants, catalysts, surface area of solid reactants, and pressure of gaseous reactants or products