What are the general formulas for alkane, alkene, alkyne, alkyl, aldehyde, ketone, cycloalkane?

Question

Brooklyn Barber · Accepted Answer

A useful idea in this context is #"the degree of unsaturation"#, which I will outline with the answer.

#"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..........

Easton Jones · Answer

undefined Alkane: CnH2n+2
Alkene: CnH2n
Alkyne: CnH2n-2
Alkyl: CnH2n+1
Aldehyde: RCHO
Ketone: RCOR'
Cycloalkane: CnH2n