In a Ph-C-CN structure the benzylic carbon is donated with electrons both by the phenyl ring and CN group.The -CN and (much less) the -Ph group
withdraw electron density. They
don't donate electrons. That's why the benzylic carboanion becomes more stable by distributing the anion charge in various possible resonance structures. Therefore, what you want is an highly electrophylic group on the benzylic or o/p-aromatic position. Electron withdrawing groups are -NR
4+, -NO
2, -CO-R, -CN, -COOR, -SO
2-R, halogens... but only a few are useful, notably those which have a stronger mesomeric than inductive effect and those which are not to electrophylic per se (read the thread
Post 490390
(politoxicomania: "P2P-derivate related", Methods Discourse) for more on this). Therefore your choice reduces to only a few: -NO2, -CN, -SO2R.
I want something that will form an ester with benzyl alcohol (...) that it wont be torn off by the NaEthoxide while activating the benzylic carbon so that it will be deprotonated by the baseSome esters can withdraw electrons trough the inductive efects (halogenides and pseudohalogenides) but they don't have any mesomeric effect and are therefore useless since they react with nucleophylic bases only as electrophyls (except for the Darzen's reaction, but there you also have the -COOR in addition to the halogen).