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Orgo 2213 Topic 9 Notes.docx

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Chemistry 1027A/B
Mel Usselman

Key Concepts In Organic Chemistry: Aldehydes & Ketones (Usselman Version) -Present in aldehydes and ketones, the carbonyl group is the most important functional group in organic chemistry. It is a carbonyl group is a polar double bond (so it can attract and initiate reaction with both electrophiles and nucleophiles). In aldehydes, the C = O of the aldehyde is always given position #1 and is given the suffix al. When the -CHO is a substituent on a ring, the suffix carbaldehyde is attached to the name of the compound. -In ketones, the C = O is given the lowest possible # in carbon chain, and the suffix –one is added. In compounds with two or more carbonyl substituents, it is termed an oxo group. In spectroscopy, the C = O has a strong distinctive stretching vibration between 1705 and 1780 cm . In proton NMR, the H atom attached to the carbonyl group of an aldehyde is shifted far downfield to 9.5-10 ppm. -Nucleophilic addition reactions are the defining reactions of carbonyl compounds where the Nu always adds to the carbon and the electrophile to the oxygen atom. The mechanism is slightly different in acid solution (where cations exist) and basic solution (where anions exist). The slow, RDS step is the breaking of the π bond by the Nu. When a stereocentre is formed, both enantiomers will be formed in equal amounts (a racemic mixture is produced). Carbonyl addition reactions are not as exothermic as alkene addition reactions and thus the reaction can be easily reduced. In general, aldehydes react faster than ketones. -In the Grignard reaction the organomagnesium compound contains a C atom with a partial negative charge. The formation of Grignard reagents is always done in ether solvents. Such organomagnesium solvents have come to be known as Grignard reagents. In the reagent, the negatively-charged alkyl group acts as a Nu and the positively-charged Mg acts as an electrophile. Grignard reactions give alcohols as products; two of the R groups on the C-OH come from the carbonyl reagent, the other from the Grignard reagent. The Grignard reaction is one of the most useful methods to create new C-C bonds in multi-step syntheses. -The product of the addition of alcohols (hemiacetal formation) contains both an OR and an OH bonded to the same C atom and is called a hemiacetal. Hemiacetal formation is catalyzed by either acid or base and is readily reversible. Exposure to either acid or base causes the hemiacetal to revert to carbonyl compound and alcohol. -In acid solution, hemiacetals react further with an alcohol by an S N substitution process to yield a compound with a C atom bonded to two OR grou
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