Chapter 10: Unit 2. Features of Organic Compounds

Features of organic Compounds

Carbon atom bonding characteristics: Carbon atoms in organic compounds must have four bonds.

1. By bonding to four other atoms: This situation requires the presence of four single bonds

2. By bonding to three other atoms: This situation requires the presence of two single bonds and one double bonds.

3. By bonding to two other atoms: This situation requires the presence of either two double bonds, or a triple bond and a single bond.

Organic compounds may also contain elements other than carbon and hydrogen. Any atom that is not carbon or hydrogen is called a hetero atom. Each hetero atom forms a characteristic number of bonds, determined by its location in the periodic table.  Common hetero atoms also have non-bonding, lone pair of electrons so each atom is surrounded by eight atoms.

Sometimes organic compounds form straight chain or ring compounds by joining them together forming a closed loop. They are called acyclic and cyclic compounds respectively. Hydrocarbons are also classified as two broad groups: aliphatic and aromatic. Aliphatic compounds doesn’t contain the hydrocarbon called benzene. Aromatic compounds must contain benzene as a part of the structure. Properties vary widely depending on aliphatic or aromatic nature of the compounds.

Shapes of Organic Compounds:

According to VSEPR theory, most stable arrangement keeps these groups far away from each other as possible.

A solid line is used for bonds in the plane.

A wedge is used for a bond out of plane.

A dashed wedge is used for a bond behind the plane.

All carbons having four single bonds are tetrahedral.  Any carbon with one double and one single bond will have trigonal planar geometry and carbon atoms with triple bond is linear in shape. Corresponding bond angles are mentioned above.

Representation:

Structural formula: Structural formulas are two dimensional representations of the arrangements of the arrangements of the atoms in molecules. These formulas give complete information about the arrangement of the atoms in a molecule but not the spatial orientation of the atoms. Two types of structural formulas are commonly encountered, expanded and condensed.

Condensed structure: All the atoms are drawn in, but the two-electron bond lines are generally omitted. To interpret a condensed formula it is usually best to start from the left side of the molecule and remember the carbon atom must have the four bonds. A carbon bonded to 3 H’s becomes CH₃, when bonded to 2 H’s becomes CH₂ and when bonded to 1 H becomes CH

Line-angle(skeletal) formula: A line-angle formula is a structural representation in which a line represents a carbon carbon bond and a carbon atom is understood to be present at every point where two lines meet and at the ends of the line. Line-angle formulas are the most concise method for representing the structure of a hydrocarbon or hydrocarbon derivative. We assume that there are enough hydrogen ats around each carbon to give it four bonds. We also need to show all the hetero-atoms and the hydrogen directly bonded to them.