A Question on Esters experiment

[dooyeon1998]

Hello
Our school did an experiment on esters and we produced Ethyl Ethanoate, Ethyl Octanoate, Pentyl Ethanoate and Pentyl Octanoate.
All of them produced expected odours except for Pentyl Octanoate. It was predicted that it would smell like Cognac or Coconut, however it smelled more like petrol. What would be a possible reasoning for this? I know that since we added the esters into cold water after the reaction, the presence of water would have driven the reaction backwards. But if that is the case, why didn't the rest of the esters also smelled different to the predictions.

Thank you

[dylzza_3011]

the chart with all the smells is just a guide, remember.
But your right it should smell like coconut. A reason may be that the ratios of the alkanoic acid and alkanol may be off, leaving you with unreacted reagents which could produce the petrol smell. Also generally once the ester is formed (especially the smaller esters, as there quite stable) the reaction reversing doesn't tend to be significant at all. Just because a reasonable unit of energy would be required to do so, and your not gonna get that in cold water plus pentyl octanoate isn't really that soluble in water so a water molecule would have a hard time colliding with the ester link. Though its not hard and fast, some of the esters may hydrolyse, but not enough for it to be significant in producing the alternate smell, like I said its most likely unreacted reagents present.