Structures of Alkanes

Naming, Drawing, and Structural Formulae for Alkanes

Alkanes• Also known as saturated hydrocarbons• Made on C and H• In hydrocarbons C is bonded to H and maybe C while H is only bonded to C• C has 4 valence electrons and needs to share another 4 electrons to make

an octet

Consider Methane with the formula CH4 this is the simplest alkane

CH4

Lewis dot structure

Complete Structural formula

Condensed structural formula

3-dimensional structure

Names of AlkanesThe names all end in “ane”, the prefix depends on how many carbons are in the alkane

Constitutional Isomers

• When the molecular formula can be drawn with different structures

• Consider butane C4H10

complete structural formulae

geometric formula

Cycloalkanes• In a cycloalkane a group of C atoms form a ring• Consider Cyclobutane C4H8

Complete StructuralFormula

Geometric Formula

CondensedFormula

3-dimensionalstructure

Haloalkanes

• In a haloalkane a halogen like Cl or Br replaces one of the H atoms in the alkane

CH3Cl Chloromethane

BrCH2CH2Br 1,2 dibromoethane

A. Structure of Alkanes• Make a model and write out (i) the 3-d structure, (ii) complete structure

formula and (iii) condensed structural formula for• CH4 (methane), C2H6 (ethane), and C3H8 (propane)

B. Constitution isomers• Make a model and write out (i) the 3-d structure, (ii) complete structure

formula and (iii) condensed structural formula for• C4H10 (butane), and 2-methyl-propane (isobutane)

• The 3 isomers of pentane C5H12

C. Cycloalkanes• Make a model and write out (i) the 3-d structure, (ii) complete structure

formula and (iii) condensed structural formula for• A ring structure involving 3 carbon atoms• A ring structure involving 5 carbon atoms

D. Haloalkanes• Make a model and write out (i) the 3-d structure, (ii) complete structure

formula and (iii) condensed structural formula for• Chloromethane, 1,2 dibromoethane, 2-iodopropane, 4 isomers of

dichloropropane