Formulas of Hydrocarbons and Isomers The adventure continues

Molecular Formulas The general formula for an alkane is: C n H 2n+2 The molecular formula indicates the atoms present and their amounts.

Structural Formula Structural formulas are two dimensional structural representations of how the various atoms of a molecule are bound to one another. Structural formulas are two dimensional structural representations of how the various atoms of a molecule are bound to one another. Structural formulas show every atom and every bond. Structural formulas show every atom and every bond.

Examples Find the structural formula for… Find the structural formula for… C 2 H 6 C 2 H 6 C 8 H 18 C 8 H 18 C 4 H 10 C 4 H 10

Two types of structural formulas The expanded structural formula. The expanded structural formula. This is what we have looked at so far. This is what we have looked at so far. The condensed structural formula. The condensed structural formula. This uses groups of atoms in which the central atoms and those connected are added in groups. This uses groups of atoms in which the central atoms and those connected are added in groups.

Condensed formulas We may condense these formulas even further. We may condense these formulas even further. CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3 May be written as: May be written as: CH 3 (CH 2 ) 2 CH 3 CH 3 (CH 2 ) 2 CH 3

Also: Expanded structural formulas show all bonds in the molecule. Expanded structural formulas show all bonds in the molecule. Some condensed structural formulas show only certain bonds between carbons. Some condensed structural formulas show only certain bonds between carbons. A skeletal structural formula shows only the bonds between carbons. A skeletal structural formula shows only the bonds between carbons. It omits the Hydrogen. It omits the Hydrogen. Therefore: Therefore: CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3 Means Means CH 3 (CH 2 ) 2 CH 3 CH 3 (CH 2 ) 2 CH 3 Means Means C-C-C-C C-C-C-C The C makes 4 bonds. The H’s are assumed The C makes 4 bonds. The H’s are assumed

Isomers Molecular formulas tell you only how many of each atom is in the molecule. Molecular formulas tell you only how many of each atom is in the molecule. It does not give you the arrangement. It does not give you the arrangement. C 4 H 10 has more than one possible arrangement. C 4 H 10 has more than one possible arrangement.

Isomers Isomers have different arrangements of atoms and therefore have different chemical properties. Isomers have different arrangements of atoms and therefore have different chemical properties.

Pharmaceutical Implications The larger the number of carbons in the carbon chain, the larger the number of possible isomers. The larger the number of carbons in the carbon chain, the larger the number of possible isomers. When chemists form new compounds, they must separate out all the isomers to identify the physiologically active compound. When chemists form new compounds, they must separate out all the isomers to identify the physiologically active compound.

Conformations of Alkanes Carbons bound by singles bonds may rotate around their bonds. Carbons bound by singles bonds may rotate around their bonds. Conformation is the specific three dimensional arrangement of the atoms in an organic compound. Conformation is the specific three dimensional arrangement of the atoms in an organic compound. Let’s go to the Ball and Stick model! Let’s go to the Ball and Stick model!

Not this Ball & Stick