The general name for linear or branched aliphatic hydrocarbons that contain a triple bond. Aliphatic compounds can be represented by drawing the full structures as in Figure 2 or they can be written in an abbreviated form such as CH4 for methane (1) and CH3CH2CH3 for propane (3) (the main constituent of LPG). The abbreviated form will generally be used in this lecture. Sometimes aliphatic hydrocarbons will be drawn with only the carbon backbone. When this is done it is assumed that each carbon will have enough hydrogens attached (one, two or three) to make up its four bonds. For example: Cyclic aliphatic hydrocarbons are sometimes drawn with lines joining imaginary carbons. This is a very convenient way of drawing cyclic structures. Thus, cyclohexane (2) can be drawn as: It is assumed that there are two hydrogens at each corner of the cyclic shape unless otherwise indicated.