Organic Chemistry: Tetravalence and Hybridisation

Tetravalence of Carbon and Shapes of Organic Compounds

• Covalent bonding ushered in the modern era of organic chemistry.
• Understanding molecular structure helps predict properties of organic compounds.
• Knowledge of valency and molecular structures from Unit 4 is assumed.

Hybridisation and Bond Length/Enthalpy

• Hybridisation influences bond length and enthalpy
• sp hybrid orbitals contain more 's' character, leading to shorter, stronger bonds compared to sp³ hybrid orbitals.
• sp² hybrid orbitals have intermediate 's' character, and bond lengths and enthalpies are also intermediate.
• Greater 's' character in hybrid orbitals leads to higher electronegativity.

Characteristics of π Bonds

• Parallel orientation of p orbitals on adjacent atoms leads to proper sideways overlap.
• π bonds create a maximum electron overlap which makes them easily reactive.
• π bonds are located above and below the bonding atoms' plane.

Problem 12.1: σ and π Bonds

• Determining the number of σ and π bonds in given molecules requires examining C-C and C-H bonds.
• Provided example solutions demonstrate the calculation method for HC≡CCH=CHCH₃ and CH₂=C=CHCH₃ molecules.

Problem 12.2: Carbon Hybridisation in Different Compounds

• Determining the type of carbon hybridisation in different compounds.
• Examples include determining the hybridisation in CH₂Cl, (CH₃)₂CO, CH₃CN, HCONH₂, and CH₃CH=CHCN.
• Solution examples are provided for determining sp, sp², sp³ hybridisation.

Problem 12.3: Hybridisation and Molecular Shapes

• Determining the state of carbon hybridisation and then the shape of different molecules.
• Determining the carbon hybridisation in H₂C=O, CHF, and HC≡N. Example solutions are given for each molecule.