[![enter image description here][1]][1]


  [1]: http://i.stack.imgur.com/lKgRK.png

Given this compound in an acidic medium , what would get protonated first?
Would not the double bond get protonated preferentially, since oxygen is more electronegative than carbon and less willing to donate an electron pair for protonation?

I checked the ***pka*** value for the conjugate acid of  aldehyde,and it was around ***-10***,which is pretty low, and hence suggests that aldehyde would have a very ***low basicity***

Also alkene (ethene) had a pka value of around 43.

Going by this information does it not make sense for a double bond to get protnated first?



*ON the other hand, the **oxonium ion,in this case is resonance stabilised** , which would indicate that it is protonated in preference to the double bonds.*


***Which of these reasoning is correct?
And more importantly, in these situations how are we supposed to predict which factor dominates?***