comparing enthalpy change of combustion of different alcohol

[chemconfused]

:? Im having difficulty identifying how enthalpy change of combusion is affected by their molecular structure. the results i have are shown as follows:

Methanol –
-316.24 kJmol-1
Ethanol –
-910.0 kJmol-1
Propan-1-ol –
-733.98 kJmol-1
Butan-1-ol –
-1077.03 kJmol-1

as you can see there is some anomalies but can anyone help me with the pattern ? i think that ethanol is an anomalie and they should increase but can anyone help me with a more scientific explanation?
many thanks
R :wink: