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8B_handout_feb2 - Chem 8B winter 2009 Details for Jan...

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Chem 8B, winter 2009, Details for Jan 25-Feb 2, 2009 Polarity of aldehydes and ketones; reactivity as electrophiles 1) Be able to draw the resonance structure of a carbonyl to explain why the carbon is electrophilic 2) Look at steric effects : bigger/bulky groups will block the addition of a nucleophile because the electrophilic carbon site is less accessible. (be able to compare/rank reactivity) These steric effects are similar to the nucleophilic substitution rxns we discussed in Chem 8A (page 234) 3) Look at electronic effects: an electron-withdrawing group (EWG) will make a carbonyl MORE electrophilic, while an electron-donating group (EDG) will make a carbonyl LESS electrophilic (be able to compare/rank reactivity) 4) The polar C=O bond has strong dipole-dipole effects that influence boiling point and solubility properties of carbonyls, review dipole-dipole effects. The C=O bond has a stronger dipole than the C-O bond, so it will have stronger dipole-dipole interactions, and thus a higher BP. There are no hydrogen-
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