ATAR Notes: Forum
HSC Stuff => HSC Science Stuff => HSC Subjects + Help => HSC Chemistry => Topic started by: Matth3wliu on June 03, 2020, 06:52:50 pm
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Hey all,
Can someone please explain why tertiary alcohols are the most reactive? i.e. with hydrogen halides
Thanks, matt
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Hey all,
Can someone please explain why tertiary alcohols are the most reactive? i.e. with hydrogen halides
Thanks, matt
Hey!
To understand this, let's split the alcohol up into the hydroxide component (\( \text{OH}^- \)) and the carbon component, which we call the carbocation. The carbocation is positive and the hydroxide is negative.
(https://i.ibb.co/JkxsHW9/IMG-2-C6-E09343172-1.jpg)
In the carbocation of the tertiary alcohol, there are three alkyl groups attached. These three alkyl groups increase the positivity of the carbocation ie. makes the carbocation more positive. Now let's bring the oxygen and carbocation back together.
Because of the increased positive charge of the carbocation, there is a bigger difference in charge between the carbocation and the hydroxide. Hence, the polarity of the C-O bond increases, as both carbocation and hydroxide are "trying to get away from each other" due to the bigger difference in charge (remember that positive and negative repel). This is why tertiary alcohols are the most reactive of the bunch. The reactivity of primary and secondary alcohols are lower as they contain fewer alkyl groups, so they are less positive and so don't increase the positive charge of the carbocation as much.
I should mention that the reason behind the alkyl groups increasing the overall positive charge of the carbocation is due to something we call the "inductive effect", which you don't really need to know.
Hope that helps! I hope other people answer this, as I have sort of simplified the actual chemistry behind this. But this should give you a general idea of why reactivity is higher in tertiary alcohols.