1 / 18

CH105.2 Part 1: Problem Solving in Organic Chemistry

CH105.2 Part 1: Problem Solving in Organic Chemistry. Carbon Intermediate Types. Before anything else…. Remember that organic reactions, no matter how difficult they may seem, simply involve the reaction between positive/partial positive and negative/partial negative sites.

damien
Download Presentation

CH105.2 Part 1: Problem Solving in Organic Chemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. CH105.2Part 1: Problem Solving in Organic Chemistry Carbon Intermediate Types

  2. Before anything else… • Remember that organic reactions, no matter how difficult they may seem, simply involve the reaction between positive/partial positive and negative/partial negative sites. • After determining these sites, three-dimensional steric considerations come into play. Ok? 

  3. One way of looking at reactions… What type of intermediate is formed? • Carbocation • Carbanion • Radical • Special Intermediate: Benzyne

  4. CARBOCATIONS in reactions… • Combine with nucleophiles (positive + negative or partial negative) • Lose proton (elimination) • Rearrangement (more stable carbocation) • General observation: mainly (but NOT exclusively) involves alkenes

  5. Carbocations in reactions… SN1 and E1 • Key step in both: formation of carbocation • SN1: combine with nucleophile • E1: lose proton

  6. Carbocations in reactions… Addition to Alkenes • Straightforward carbocation formation: hydrogen halide addition

  7. Carbocations in reactions… Addition to Alkenes • Variations of carbocation formation: cationic 3-membered ring intermediate • The more substituted carbon can then be attacked by a nucleophile to form the addition product • X2 addition; halohydrin formation; oxymercuration

  8. Carbocations in reactions… Addition to Alkenes • Variations of carbocation formation: 4-membered ring transition state (Henson, pakidrawingnalang, hindikoalampaanosachemsketch eh. Haha) • HYDROBORATION

  9. Carbocations in reactions… • Acid catalyzed dehydration of alcohols • Electrophilic aromatic substitution

  10. Carbocations in reactions… • Hydrolysis of tert-butyl esters (vs. usual mechanism) • Diazotization • Carbocation may undergo each of the 3 processes

  11. Carbocations in reactions… • Pinacol rearrangement • Acid-catalyzed polymerization of alkenes

  12. CARBANIONS in reactions… • Acts as base (abstracts proton) • Acts as nucleophile (reacts with electrophiles) • General observation: involves • Substitution with carbon nucleophiles • Organometallic reagents • Carbonyl chemistry

  13. Carbanions in reactions… • SN2 with CN- as nucleophile • Nucleophilic aromatic substitution • Carbanion intermediate formed: Meisenheimer complex • Grignard reagent • + H2O = alkane • + aldehyde, ketone, ester = alcohol • + RCΞN = ketone

  14. Carbanions in reactions… • Gilman reagent (diorganocopper lithium) R2CuLi + R’X → R-R’ • 1,2 and 1,4 addition to α,β-unsaturated carbonyls: governed by HARD-HARD/SOFT-SOFT chemistry • Carbonyl, C=O: hard (direct 1,2-addition by hard :Nu) e.g. Grignard reagent • Alkene, C=C: soft (conjugate 1,4-addition by soft :Nu) e.g. Gilman reagent

  15. Carbanions in reactions… • Carbonyl α-substitution reactions • Usually by aldehydes, ketones, and esters, especially β-DIKETONES and β-KETO ESTERS • Common reactions: • Halogenation of α-position • Monohalogenation in acidic medium • Multiple halogenation in basic medium (excess halogen: Haloform reaction occurs) • Hell-Volhard-Zelinski Reaction (Br2, PBr3) • If 2nd step is H2O = α-brominated carboxylic acid • If 2nd step is ROH = α-brominated ester • If 2nd step is excess NH3 = α-amino acid

  16. Carbanions in reactions… • Carbonyl α-substitution reactions • Common reactions: • Alkylation of α-position • Direct alkylation (SN2 with CH3I) • Malonic and acetoacetic ester synthesis

  17. RADICALS in reactions… • Combine with another free radical Br• + Br• → Br–Br • Abstract an atom from a molecule RO• + H–Br → ROH + Br• • Add to an unsaturated molecule • Decompose into 2 fragments R–COO• → R• + CO2

  18. Radicals in reactions… • Indicators of a radical reaction: • Radical initiators: benzoyl peroxide or AIBN • Heat or light may also initiate radical formation

More Related