Formulas of Hydrocarbons Formulas of Hydrocarbons and Isomersand Isomers

The adventure continuesThe adventure continues

Molecular FormulasMolecular Formulas

The general formula for an alkane is: CnH2n+2

The molecular formula indicates the atoms present and their amounts.

Structural FormulaStructural Formula

Structural formulas are Structural formulas are two dimensional two dimensional structural structural representations of how representations of how the various atoms of a the various atoms of a molecule are bound to molecule are bound to one another. one another.

Structural formulas Structural formulas show every atom and show every atom and every bond.every bond.

ExamplesExamples

Find the structural Find the structural formula for…formula for…

CC22HH66

CC88HH1818

CC44HH1010

Two types of structural formulasTwo types of structural formulas The expanded The expanded

structural formula.structural formula. This is what we have This is what we have

looked at so far.looked at so far. The condensed The condensed

structural formula.structural formula. This uses groups of This uses groups of

atoms in which the atoms in which the central atoms and central atoms and those connected are those connected are added in groups.added in groups.

Condensed formulasCondensed formulas

We may condense these We may condense these formulas even further.formulas even further.

CHCH33CHCH22CHCH22CHCH33

May be written as:May be written as: CHCH33(CH(CH22))22CHCH33

Also:Also: Expanded structural Expanded structural

formulas show all bonds formulas show all bonds in the molecule.in the molecule.

Some condensed Some condensed structural formulas structural formulas show only certain bonds show only certain bonds between carbons.between carbons.

A skeletal structural A skeletal structural formula shows only the formula shows only the bonds between carbons.bonds between carbons.

It omits the Hydrogen.It omits the Hydrogen.

Therefore:Therefore:

CHCH33CHCH22CHCH22CHCH33 MeansMeans

CHCH33(CH(CH22))22CHCH33 MeansMeans C-C-C-CC-C-C-C The C makes 4 The C makes 4

bonds. The H’s are bonds. The H’s are assumedassumed

IsomersIsomers

Molecular formulas tell Molecular formulas tell you only how many of you only how many of each atom is in the each atom is in the molecule.molecule.

It does not give you the It does not give you the arrangement.arrangement.

CC44HH1010 has more than one has more than one

possible arrangement.possible arrangement.

IsomersIsomers

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

Pharmaceutical ImplicationsPharmaceutical Implications

The larger the number The larger the number of carbons in the carbon of carbons in the carbon chain, the larger the chain, the larger the number of possible number of possible isomers.isomers.

When chemists form When chemists form new compounds, they new compounds, they must separate out all the must separate out all the isomers to identify the isomers to identify the physiologically active physiologically active compound.compound.

Conformations of AlkanesConformations of Alkanes

Carbons bound by singles bonds may rotate Carbons bound by singles bonds may rotate around their bonds. around their bonds.

Conformation is the specific three dimensional Conformation is the specific three dimensional arrangement of the atoms in an organic arrangement of the atoms in an organic compound.compound.

Let’s go to the Ball and Stick model!Let’s go to the Ball and Stick model!

Not this Ball & StickNot this Ball & Stick