EWG_EDG_ans

EWG_EDG_ans - EWD-EDG Worksheet Let's review the concepts...

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EWD-EDG Worksheet Let’s review the concepts behind (EWG) R and (EDG) R . Certain structural groups can withdraw or add electron density by resonance effects. Resonance effects occur though π -bonds (or empty p-orbitals) and lone pair electrons. Thus, groups that can exert a resonance effect will have π - bonds (or empty p-orbitals) or lone pair electrons. For a list of (EWG) R and (EDG) R , look here: http://myweb.unomaha.edu/~dstack/2250/Overheads/EWG_EDG.PDF . In order for an (EWG) R or (EDG) R to have an effect on a system, e.g. the acidity of a proton, it must be located at the proper proximity to that system. For example, consider a proton on atom “Y” that when forming a conjugate base generates an anion. The (EWG) R or (EDG) R needs to be adjacent to “Y” not part of “Y”. Consider the two compounds below. Structure A has a pKa of 19 while B is an extremely weak acid. Both have a carbon involved in a π -bond, but only A has the (EWG) R located in the proper proximity (i.e. adjacent to “Y”). HY Z - Y Z -H + (EWG) R or (EDG) R CH 3 C O CH 3 H C O H -H + CH 3 C O CH 2 CH 3 C O CH 2 (EWG) R adjacent to "Y" -H + H C O no resonance delocalization A (EWG) R is on "Y" pKa = 19 pKa > 40 B
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1. Each of the following compounds has an (EWG) R . a) Circle the (EWG) r . b) Identify which
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This note was uploaded on 09/03/2009 for the course CHEM 2250 taught by Professor Stack during the Spring '09 term at UNO.

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EWG_EDG_ans - EWD-EDG Worksheet Let's review the concepts...

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