Alkanes and Cycloalkanes



Alkanes and cycloalkanes are hydrocarbons in which all of the bonds are single bonds. Alkanes are predominantly produced by decomposing organic material, and they are used as fuel and solvents. Organic molecules such as alkanes are named using the IUPAC system, which involves adding suffixes and prefixes to the parent name to show the location of substituent groups on the molecule. Intermolecular forces are weak or nonexistent in alkanes, and as a result, alkanes have low melting and boiling points and poor solubility in water. Alkanes can be drawn using Newman projections, sawhorse structures, and wedge-and-dash drawings. Conformational analysis helps predict a molecule's stability based on its bond angles. Cyclic alkanes can experience ring strain due to deviations from the optimal 109.5° bond angle. Cyclohexane, the most common and stable cyclic ring, adopts two nonplanar conformations: the chair and the boat. Substituents adopt axial and equatorial positions depending on which carbon atom they are bonded to, and molecules can either be cis or trans, depending on whether the substituents are located on the same side or opposite sides of the ring.

At A Glance

  • IUPAC rules are used to give each organic molecule a unique name. Rules involve determining the name of the parent structure and then adding a modifying suffix to the name based on functional groups. Then substituents' names and locations are added as prefixes with a number, or locant, that indicates their location on the parent structure.
  • The main source of alkanes is petroleum from decomposed organic material. Alkanes are used for a variety of purposes. Alkanes have very weak intermolecular forces and, as a result, have low melting and boiling points and poor water solubility.
  • To visualize a molecule in three dimensions, a wedge and dash can be used on a bond line formula to show orientation of the groups. Sawhorse structures and Newman projections can also be used to show the three-dimensional view of molecules.
  • Ring strain is a combination of angle strain (deviation from the ideal tetrahedral angle) and torsional strain (eclipsing groups in ring form) that most rings will have due to forming cyclic structures.
  • The bond line cyclohexane form represents a 2-D view of a cyclic structure. The chair represents a 2-D representation of the 3-D reality of the molecule.