Ch 12 Notes

Ch 12 Notes - The Story of the Hydride Molecular Structure...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
The Story of the Hydride
Background image of page 1

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

View Full DocumentRight Arrow Icon
Molecular Structure (refresher) 2 H's 2 H's ! Csp 2 Csp 2 ! Csp 2 Hs Csp 2 p Csp 2 p ! Csp 2 Hs " CpCp "# CpCp !# Csp 2 Csp 2 !# Csp 2 Hs !# Csp 2 Hs ! Csp 2 Csp 2 ! Csp 2 Hs ! Csp 2 Hs " CpCp MO MO MO H H H H
Background image of page 2
Molecular Structure (refresher) 2 H's ! Csp 2 Osp 2 ! Csp 2 Hs Csp 2 p Osp 2 p LP Osp 2 " CpOp "# CpOp !# Csp 2 Osp 2 !# Csp 2 Hs ! Csp 2 Osp 2 ! Csp 2 Hs " CpCp MO MO MO H H
Background image of page 3

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

View Full DocumentRight Arrow Icon
Introduction The carbonyl group is found in several functional groups: By one or more steps, alcohols may be transformed into these types of compounds, and, in turn, these functional groups may be transformed into alcohols. CHOH R R' C=O : R R' oxidation reduction R'O aldehyde ketone carboxylic acid ester C=O R H C=O R R' C=O R HO C=O R Alcohols from Carbonyl Compounds. Oxidation-Reduction and Organometallic Compounds.
Background image of page 4
Reactions with Nucleophiles Nucleophilic additions to the carbonyl function are common. The nucleophile (Nu: - ) is attracted to the electropositive carbon where bonding is initiated through interaction with the p z orbital. Nu: - + C O ! + !" = sp 2 : C O 120 o 120 o The carbonyl group is locally planar. Nu : - sp 3 C O Attack on C-O ! " C-O ! is like an "intramolecular leaving group" N u g
Background image of page 5

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

View Full DocumentRight Arrow Icon
Hydride Ion and Carbanions as Nucleophiles Two important nucleophiles in reactions with carbonyl functions are: Hydride ions are readily available from the metal hydride reagents : Carbanions are available from organometallic reagents such as: hydride ion carbanions H: - R: - - sodium borohydride (sodium tetrahydridoborate) - lithium aluminum hydride (lithium tetrahydridoaluminate) Na + H-B-H H H Li + H-Al-H H H organolithium organomagnesium halide R-Li R-MgX
Background image of page 6
Formal Oxidation States A formal oxidation state may be assigned to a carbon as follows: • A bond to another carbon is 0 (zero). • A bond to H (or anything less electronegative) is -1. • A bond to a more electronegative atom (O, N, halogen) is +1. Example: For the sequence The formal oxidation states at C are: C C C R-C-H R-C-OH R-C-H = R-C-OH H H H H [H] [O] [H] [O] [H] [O] O O (-3) (-1) (+1) (+3)
Background image of page 7

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

View Full DocumentRight Arrow Icon
Reactions of Lithium Aluminum Hydride R-C-R' O = : : + Li + H-Al-H H H - hydride addition ether solvent H 2 O (workup) R-C-H R' O H + Al(OH) 3 + LiOH Stoichiometry 4 R-C-R' O : : + LiAlH 4 R-C- H R' O Al 4 - All 4 H are active. a tetraalkoxyaluminate 4 H 2 O R-C- H R' O H + Al(OH) 3 + LiOH 4 R-C-H - R' O AlH 3 Li +
Background image of page 8
Esters: A Two-stage Reduction (2) R-C-H O = : : aldehyde Li -Al-H - + + ether solvent Overall Stoichiometry 2R-C-OR' O : : + LiAlH 4 All 4 H are active. RC H 2 O-Al OCH 2 R OR' OR' - Li + H 2 O (workup) RC H 2 OH + R'OH + Al(OH) 3 + LiOH 2 2 R-C-H : : aldehyde + R'O-Al - O H H H Li + R-C-OR' : : + - (1) O Li + H-Al-H H H R-C-H - H O Al Li +
Background image of page 9

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

View Full DocumentRight Arrow Icon
Carboxylic Acids As with esters, carboxylic acids are reduced to primary alcohols derived from the carboxyl function. A fast, initial acid-base reaction gives the carboxylate salt which is reduced by LAH. RCOH O = + LiAlH 4 RCO 2 - + Li + H 2 + AlH 3 fast The key reduction step may occur via: R-C O H R-C- O H H - further reduction Overall Stoichiometry 4 RCO 2 H + 3 LiAlH 4 ether solvent [RCH 2 O] 4 Al - + Li + 4 H 2 + 2 LiAlO 2 (H 2 O) workup 4 RCH 2 OH + Al(OH) 3 + LiOH primary alcohol R-C - O OAlH 3 H -Al -
Background image of page 10
Some Examples of LAH Reductions O = (i) LiAlH 4
Background image of page 11

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

View Full DocumentRight Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/04/2010 for the course CHEM 322AL at USC.

Page1 / 67

Ch 12 Notes - The Story of the Hydride Molecular Structure...

This preview shows document pages 1 - 12. Sign up to view the full document.

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