Chapter 9 Aldehydes and Ketones

1. Chemistry 20 Chapter 9 Aldehydes and Ketones

2. O = C Carbonyl group Aldehydes Ketones Carboxylic acids Esters

3. Aldehydes and Ketones O = C • In an aldehyde, at least one H atom is attached to a carbonyl group. • In a ketone, two carbon groups are attached to a carbonyl group.

4. Naming Aldehydes Step 1 Select the longest carbon chain that contains the carbonyl group (C=O). Step 2 Number from the end nearest C=O group. Step 3 Change the ending of parent alkane from -e to -al. No number for carbonyl group C=O (it always comes first). Step 4 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain.

5. Naming Aldehydes • Common names for the first two aldehydes use the prefixes “form” (1C) and “acet” (2C)followed by “aldehyde”. • H─C─H CH3─ C ─H CH3─CH2─ C ─H • methanal ethanal propanal • (formaldehyde) (acetaldehyde) O O O = = =

6. CH3─CH─CH2─ C─H 3-Methylbutanal • Cl─CH2─CH2─ C─H 3-Chloropropanal CH3 O = 4 3 2 1 O = 3 2 1

7. Naming Ketones Step 1 Select the longest carbon chain that contains the carbonyl group (C=O). Step 2 Number from the end nearest C=O group. Step 3 Change the ending of parent alkane from -e to -one. Use the number to show the location of C=O. Step 4 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain.

8. Naming Ketones • In the common name, name the “alkyl groups” alphabetically attached to the carbonyl group and add the word “ketone”. • CH3 ─ C ─CH3 CH3─C─CH2─CH3 • Propanone 2-Butanone • (dimethyl ketone) (ethyl methyl ketone) O O = = 2 1 3 4

9. 3-Chloro Cl

11. δ- δ+ δ- δ+ Physical properties of Aldehydes and Ketones • They have strong odors (ketones have pleasant odors). • They are polar compounds. • Only dipole-dipole interactions (no hydrogen bonding). • Low boiling points compare to amines and alcohols. • Soluble in water (no soluble in nonpolar compounds). C-O 3.5-2.5 = 1 Higher than hydrocarbons. H O δ+ H Hydrogen bond with water.

12. O = CH3─CH2─CH2─CH2─C─H Pentanal Liquid aldehydes are sensetive to oxidation. No oxidizing agent Chemical properties of Aldehydes and Ketones 1. Oxidation: only for aldehydes (not for ketones). O K2Cr2O7 = CH3─CH2─CH2─CH2─C─OH H2SO4 Pentanoic acid K2Cr2O7: Oxidizing agent

13. Tollen’s Test (Silver-mirror test) Tollens’ reagent is specific for the oxidation of aldehydes (not for ketones).

14. t r a n s i t i o n m e t a l c a t a l y s t H 2 1 - P e n t a n o l t r a n s i t i o n O OH m e t a l c a t a l y s t = - H + CH3─CH─CH2─CH3 CH3─C─CH2─CH3 2 2-butanol 2-butanone Chemical properties of Aldehydes and Ketones 2. Reduction: • Like reducing the alkene (C = C) to alkane (C – C): • Reduction of an aldehyde gives a primary alcohol (-CH2OH). • Reduction of a ketone gives a secondary alcohol (-CHOH-). O = + CH3─CH2─CH2─CH2─C─ H CH3─CH2─CH2─CH2─CH2─ OH Pentanal

15. Chemical properties of Aldehydes and Ketones NaBH4 Sodium borohydride: produces hydride ion: H- Reducing agent Reduction mechanism: -

16. Chemical properties of Aldehydes and Ketones Advantage of NaBH4: Reduction by NaBH4 does not affect a carbon-carbon double bond or an aromatic ring. H3O+

17. Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (hemiacetals): H of the alcohol adds to the carbonyl oxygen and OR adds to the carbonyl carbon. unstable

18. O O - CH2CH3 H O - C H C H O O C C H H C C H H 2 2 3 3 2 3 E t h a n o l A h e m i a c e t a l Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (Acetals): Acid C + H C H2O + H H An Acetal

19. Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (hemiacetals): If –OH is part of the same molecule that contains C=O.