Ch_322a_3.017

Ch_322a_3.017 - same base strength and are comparably...

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Organic Compounds as Bases All organic compounds with an unshared electron pair , or a ! - bond are potential bases. CH 3 -O: H : + H-Cl: :: methanol (base) (acid) CH 3 -OH 2 + + Cl - When HCl gas is dissolved in methanol, it dissociates by protonation of the oxygen in the alcohol. This is a general reaction between alcohols and strong acids (HX, H 2 SO 4 ) analogous to the ionization of strong acids in water. R-O: H + H-A strong acid ROH 2 + + :A -
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Ethers react in a similar way: R-O: R' : + H-A strong acid R-O-H R' + + :A - C :O: = R R' + H-A weak base strong acid C :O R R' H + + :A - conjugate acid (a very strong acid) Carbonyl compounds are involved in an equilibrium with strong acids that produces a low concentration of the conjugate acids: The table that follows compares the base strength of carbonyl compounds, alcohols, ethers and water . The latter three have about the
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Unformatted text preview: same base strength and are comparably protonated by strong acids. Carbonyl compounds are considerably weaker bases (factor of 10 4 to 10 5 ). Some Representative pK B and pK BH + Values Base pK B Conjugate Acid pK BH + R-C=O R : ketone 21 R-C=O R H-7 + R-O R ether 17.5 R-O R H-3.5 + RCH 2 O H alcohol 16 RCH 2 O H H-2 + H-O H water 15.74 H-O H H-1.74 + weakest base strongest acid H-O hydroxide ion-2-H-O H 16 Alkenes as !-Bases Strong acids react with alkenes in an equilibrium: C=C + H-A C-C H + + :A-In this reaction, the polarizable !-electrons are used to form the C-H sigma bond: C C + H-A ! + !" C C H + + :A-a carbocation Many reactions of alkenes are initiated by the !-electrons acting as a base....
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_3.017 - same base strength and are comparably...

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