#"Alkanes:"# #C_nH_(2n+2)#;

#"Alkene:"# #C_nH_(2n)#;

#"Alkyne:"# #C_nH_(2n-2)#;

#"Alkyl residue:"# #C_nH_(2n+1)#;

#"Aldehyde/ketone:"# #C_nH_(2n)O#;

#"Cycloalkane:"# #C_nH_(2n)#

A fully saturated hydrocarbon, an alkane, has general formula #C_nH_(2n+2)#: #n =1#, methane; #n =2#, ethane; #n =3#, propane. BY reason of their formula alkanes are said to #"HAVE NO DEGREES of UNSATURATION."#

Where the formula is #C_nH_(2n)# or #C_nH_(2n)O_m#, each 2 hydrogens LESS than #2n+2# represents a #"degree of unsaturation"#. Each degree of unsaturation represents a double bond OR a ring. Compare cyclopropane to propane or hexane to cyclohexane to cyclohexene; does this formulation hold?

Where there is nitrogen in the formula we substract #NH# from the given formula before assessing its degree of saturation. For #"methylamine"#, #H_3CH_2CNH_2#, we assess a formula of #C_2H_6#, no degrees of saturation. For pyridine, #C_5H_5N#, we assess #C_5H_4#, #4^@# of unsaturation, i.e. 3 olefinic bonds, and one ring..........