BonusHW01Key - localized on a larger atom. The negative...

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Bonus HW Problem #01 – Answer Key This “bonus” homework problem is worth 20 raw points. Remember, at the end of the semester, only your 15 highest homework scores will be counted (as 10% of your final course grade). This “extra” assignment, then, provides you with an additional opportunity to earn homework points!!! Arrange the compounds in each of the following sets in order of decreasing pK a [1 = highest pK a ; 3 = lowest pK a ]. Then, provide an explanation for your answer (use back of page if you need more space). CH 3 CH 2 OH Cl 2 CHCH 2 OH ClCH 2 CH 2 OH (a) E x p l a n a t i o n : 1 3 2 CH 3 CH 2 OH ClCH 2 CH 2 SH (b) E x p l a n a t i o n : CH 3 CH 2 SH 3 1 2 Incorporation of electronegative chlorine atoms in the molecule stabilizes the resulting conjugate base via an inductive effect. Having two chlorine atoms in the molecule is more stabilizing than having only one. Moving down a column, acidity increases because the negative charge of the conjugate is
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Unformatted text preview: localized on a larger atom. The negative charge is “spread out” over a larger volume, which stabilizes the anion. For this reason, the thiol is more acidic than the alcohol. The thiol that also contains a chlorine substituent is more acidic than the thiol that lacks a chlorine substituent, due to the inductive effect caused by the electronegative chlorine atom. (c) E x p l a n a t i o n : H As(CH 3 ) 2 H As(CH 3 ) 2 H H N(CH 3 ) 2 2 3 1 Considering the same element, positively charged molecules are more acidic than neutral molecules (the conjugate base is a neutral molecule which is more stable than an anion). As stated above, when moving down a column, acidity increases, because localization of the negative charge on a larger atom stabilizes the conjugate base anion....
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This note was uploaded on 07/16/2008 for the course CH 310M taught by Professor Iverson during the Spring '05 term at University of Texas at Austin.

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