Doc Brown's GCE Chemistry
Revising Advanced Level Organic Chemistry
GCE A Level Revision Notes PART 10 Summary of organic reaction mechanisms
A mechanistic introduction to organic chemistry and explanations of different types of organic reactions
Reduction with hydrides
Examples are explained of the organic chemistry mechanisms for aldehydes and ketones undergoing nucleophilic substitution, nucleophilic addition reactions are described with diagrams and full explanation revision notes. Carbonyl compounds – ALDEHYDES and KETONES – introduction. Nucleophilic addition of hydrogen – via reduction with LiAlH4 or NaBH4 to give alcohols. The revision notes include full diagrams and explanation of the mechanisms and the 'molecular' equation and reaction conditions and other con–current reaction pathways for these reactions of aldehydes and ketones and products are also explained.
10.6 Carbonyl compounds – ALDEHYDES and KETONES
10.6.1 Introduction to aldehyde and ketone reactivity
Aldehydes and ketones readily undergo nucleophilic attack because of the highly polar carbonyl bond >Cδ+=Oδ– caused by the big difference in the electronegativity between carbon (2.5) and oxygen (3.5). An electron pair donating nucleophile (Nuc:), will therefore attack the 'positive carbon' (Cδ+) to form a C–Nuc bond. A comparison of electrophilic addition to alkenes with nucleophilic addition to aldehydes/ketones is included in these notes.
10.6.3 Nucleophilic addition of a hydride ion in the reduction of aldehydes/ketones to primary/secondary alcohols
The organic synthesis of alcohols by the reduction of aldehydes and ketones
mechanism 40 – nucleophilic addition of a hydride ion (via NaBH4 or LiAlH4) to an aldehyde or ketone
keywords phrases: reaction conditions formula intermediates organic chemistry reaction mechanisms nucleophilic addition elimination nucleophilic substitution NaBH4 sodium tetrahydridoborate(III) LiAlH4 lithium tetrahydridoaluminate(III) (OH)CN RR'C=O + 2[H] ==> RR'CHOH XH4– + R2C=O => [H3XO–CHR2]– = R2C=O => [H2X(O–CHR2)2]– = R2C=O => [HX(–OCHR2)3]– = R2C=O => [X(–OCHR2)4] – [X(OCR2)4]– + water/acid/alcohol => 4R2CHOH
APPENDIX - COMPLETE MECHANISM and Organic Synthesis INDEX (so far!)