12. Aldehydes & Ketones

12. Aldehydes & Ketones - 2010 Department of Chemistry,...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
© 2010 Department of Chemistry, The University of Western Ontario 12.1 12. Aldehydes & Ketones (text 13.1 – 13.10) A. Structure and Nomenclature The carbonyl group is present in aldehydes and ketones and is the most important group in bio-organic chemistry. carbonyl group aldehyde ketone O O R R O H R Both the C and O are sp 2 , and their p orbitals overlap to form a bond. Angles are 120°. Most importantly, the C=O is a polar double bond . It can react with both electrophiles and nucleophiles. In IUPAC nomenclature, for a compound named as an aldehyde, the C=O is always position #1 (takes precedence over other groups) and the suffix al is used. O H O Br Br H propanal 3,3-dibromo-2-methylbutanal C O + -
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
12.2 When the one-carbon aldehyde group –CHO is a substituent on a ring, the suffix carbaldehyde is added to the ring name, and the point of attachment is given #1. CHO CHO cyclopropanecarbaldehyde cis -2-methylcyclopentanecarbaldehyde In ketones, the C=O is given the lowest possible number in the carbon chain and the suffix one is added. O 3-methyl-2-butanone O 4,4-dimethyl-2-cyclohexenone In compounds with two or more functional groups, it may be necessary to name the carbonyl group as an ordinary substituent using oxo . Carbonyl compounds don’t have a + hydrogen, so intermolecular hydrogen bonding is not possible. However, the polar carbonyl group results in higher BP than ethers, but lower than that of alcohols. O O OH 80° 35° 118° 3-oxobutanal H O O
Background image of page 2
12.3 B. Spectroscopy In IR spectroscopy, the carbonyl group has a strong, distinctive absorption between 1705 – 1780 cm −1 . (As we’ll see later, the C=O stretch appears in all functional groups containing the C=O bond, including acids and derivatives). In proton NMR, the H atom of aldehydes is shifted far downfield to about 9.5 – 10 ppm. Although the carbonyl H ( d ) splits (and is also split by) the two H atoms c , the splitting is very small. Thus, d looks like a singlet. Similarly, the signal for c looks like it is split only by the H atoms b . Note that ketones do not have an H on the C=O, so the peak near 9.5 – 10 ppm does not appear.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
12.4 C. Nucleophilic Addition Reactions The reactivity of carbonyl compounds can be explained by the structure of the carbonyl group. Nucleophiles will always add to the carbon, and electrophiles (typically a proton) to the oxygen. Therefore, only one regioisomer is formed. O R' R C O H R' R Nu O R' R The mechanism of the reaction depends on whether the solution is acidic or basic. Regardless of the mechanism, these are termed nucleophilic addition reactions because the RDS is the breaking of the bond by the nucleophile. In basic solution, where anions exist, nucleophilic attack
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/01/2011 for the course CHEMISTRY Chemistry taught by Professor Dr.felixlee during the Fall '11 term at UWO.

Page1 / 23

12. Aldehydes & Ketones - 2010 Department of Chemistry,...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online