[dun13203171]

Hi guys,
             Say you had the 5 molecules with different functional groups.

One with just a ketone, another with just an aldehyde, another with both an ether and and OH group, a carboxylic acid
And one with both an amine and a carboxylic acid.

How could you determine which molecules would be easily ionised? I have been advised this is a style of question I will be asked on Friday on an exam.

If someone could give me an insight into how to determine this it would be greatly appreciated.

[TheUnassuming]

What are you covering right now in class?  Mass spec?

[dun13203171]

Just a basic overview of organic chemistry, no mass spec as of yet. More principles of chemistry.

Im interested in information on what functional groups ionise the easiest and what functional groups form salts.

thanks

[TheUnassuming]

Ok, so to figure out which will form a cation/anion first you need to know the pka of each functional group.  There are a number of pka tables online that can tell you which functional groups will protonate or deprotonate first to form a salt.  My usual first stop is the Evans pKa table: evans.rc.fas.harvard.edu/pdf/evans_pKa_table.pdf

[dun13203171]

Thankyou very much! Your a gent.

So general, the lower the pka, the more it will ionise?

Methanoic acid, with a pka around 4 had a much greater affinty to deprotonate than its equivalent alcohol which has a pH closer to 16?

[dun13203171]

Ohh and I have been looking for the pka of an amide, for example R-NH2.

Am I right in saying since NH3 is weak acid, and if deproonated to R-NH2 (AMIDE) is the amide functional group would have a very low pkb as it would be such a strong conjugate base and hence is an easily ionised functional group?

[TheUnassuming]

(cation)

So general, the lower the pka, the more it will ionise?

The more readily it will deprotonate, not necessarily ionize if you are starting from a cation like an ammonium.