#OrganicFormula

#Chemistry

#OrganicChemistry

Introduction

• The most common formulae in Organic Chemistry are :

  • Molecular Formula

  • Empirical Formula

  • Structural Formula (Condensed Structural Formula)

  • Displayed Formula (Full Structural Formula)

  • Skeletal Formula

  • Stereochemical Formula

Empirical Formula

• Simplest formula that shows the ratio of number of atoms of the elements present in one molecule

Molecular Formula

• Shows the actual number of atoms of the elements present in one molecule

• For example, the empirical formula and molecular formula for lactic acid is CH2O and C3H6O3.

Condensed Structural Formula

• Shows how the constituent atoms of a molecule are joined together with minimal detail using conventional groups

• All the atoms attached to a particular carbon atom are written immediately after that carbon atom

• For example, the condensed structural formula for lactic acid is CH3CH(OH)CO2H and that for 2-methylpropene is CH2C(CH3)2.

Full Structural Formula (Displayed Formula)

• Detailed structure of a molecule showing the relative placing of atoms and the number & type of bonds between them

• One of the common mistake students often made is the omission of O-H bonds for the hydroxyl functional group

• For ring structures (including benzene rings), all the C and H atoms (and their related bonds) can be omitted

Skeletal Formula

• Simplified organic formula by removing hydrogen atoms from alkyl chains, leaving just the carbon skeleton and associated functional groups

• Each C-C bond in the carbon skeleton is a line (each end is a carbon atom)

• Double and triple lines indicate double and triple bonds respectively

• Note that skeletal or partial skeletal structures are acceptable in student’s answers where they are unambiguous.

Stereochemical Formula

• Shows the three-dimensional spatial arrangement of bonds, atoms and groups around a key part of a molecule (usually a stereochemical centre)

• Solid wedges indicate bonds to an atom pointing out of the plane of the paper

• Dashed wedges or hashed lines indicate bonds to an atom pointing into the plane of the paper

• Normal straight lines indicate bonds on the plane of the paper

Examples

• Lactic Acid :

• Empirical Formula - CH2O

• Molecular Formula - C₃H₆O₃

• Condensed Structural Formula - CH3CHOHCO2H

• Displayed Formula -

Skeletal Formula -

Stereochemical Formula -