Aldehydes feature an sp2hybridized, planar carbon center that is connected by a double bond to oxygen and a single bond to hydrogen. The CH bond is not acidic. Because of resonance stabilization of the conjugate base, an αhydrogen in an aldehyde (not shown in the picture above) is far more acidic, with a pKa near 17, than a CH bond in a typical alkane (pKa about 50).2 This acidification is attributed to (i) the electronwithdrawing quality of the formyl center and (ii) the fact that the conjugate base, an enolate anion, delocalizes its negative charge. Related to (i), the aldehyde group is somewhat polar. Aldehydes (except those without an alpha carbon, or without protons on the alpha carbon, such as formaldehyde and benzaldehyde) can exist in either the keto or the enol tautomer. Ketoenol tautomerism is catalyzed by either acid or base. Usually the enol is the minority tautomer, but it is more reactive.
1 ALDEHYD VAØ CETON BEÙO 2 1. Goùi teõn caực hụùp chaỏt sau: Trichloroethanal Trichloroacetaldehy d Cloral Propenal Acrolein but-2-en-1-al Crotonaldehyd Ethandial Glyoxal 5-methylhex-4-en-2-on Methylvinylceton 3-phenylpropanal pentan-2,4-dion acetoaceton 1,1-dimethoxyethan 3-oxobutanal Acetoacetandehyd 3 2,6-di (4’-hydroxy-3’-methoxybenzyl) cyclohexanol Cyclovalon(Thuốc lợi mật) 2-(2’-chlorophenyl)-2-(methylamino) cyclohexanon Ketamin 6-[(R)-2’-hydroxy-6’-methylhept-5’-en-2’-yl]cyclohex-2-en-1-on Hermanducil 6-methyl-2-(2-oxocyclohex-3-en-1-yl)hept-5-en-2-ol) 4 2. Vieát coâng thöùc caùc chaát sau: Di-tert-butylceton cyclopropanon 3-methyl-3 cyclohexen-1-on ethylbenzylceton phenylacetaldehyd methylethylallylacetaldehyd 4-cloro-4-methylpent-2-en-1-al 3-oxohexanal a. c. e. g. b. d. f. h. 5 3. Aldol hoùa: a. b. 6 4. Viết phương trình chuyển hóa a. Propen aceton b. 1-bromobutan methylethylceton CH 3 CH 2 CH 2 CH 2 Br 7 c. Propen propanal d. Cyclohexen cyclohexanon: 4. 8 5. Điều chế butanon: a. Từ 2-chlorobutan b. T ethanalừ 9 c. Từ 2,3-dichlorobutan 5. d. Từ acetonitril 10 e. Từ 1-buten 5. f. Từ 3-methyl-2-pentanol (đặ c)