Alkynes - Organic Chemistry I - Lecture Slides, Slides of Organic Chemistry

Download Alkynes - Organic Chemistry I - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Alkynes. CnH2n-2 C2H2 H:C:::C:H H—C  C—H sp => linear, 180 o acetylene ethyne C3H4 CH3CCH methylacetylene propyne docsity.com nomenclature: common names: ―alkylacetylene‖ IUPAC: parent chain = longest continuous carbon chain that contains the triple bond. alkane drop –ane add -yne prefix locant for the triple bond, etc. CH3CH2CCCH3 2-pentyne ethylmethylacetylene docsity.com Synthesis, alkynes: 1. dehydrohalogenation of vicinal dihalides H H H | | | — C — C — + KOH  — C = C — + KX + H2O | | | X X X H | — C = C — + NaNH2  — C  C — + NaX + NH3 | X docsity.com H H | | — C — C — + 2 KOH  — C  C — + KX + H2O | | heat X X CH3CH2CHCH2 + KOH; then NaNH2  CH3CH2CCH Br Br ― + 2 KOH, heat docsity.com alkene vicinal dihalide alkyne X2 1. KOH 2. NaNH2 CH3CH=CH2 CH3CHCH2 CH3CCH Br Br Br2 1. KOH 2. NaNH2 docsity.com CH3C C Na + CH3CCH3 CH3 Br CH3C CH + CH3C CH2 CH3 3o alkyl halide E2 elimination! note: R-X must be 1o or CH3 to get SN2! docsity.com   some     alkynes acids bases metals oxid. reduct. halogens terminal only terminal only docsity.com Reactions, alkynes: 1. addition of H2 (reduction) 2. addition of X2 3. addition of HX 4. addition of H2O, H + 5. as acids 6. Ag+ 7. oxidation docsity.com CH3 H \ / Na or Li C = C anti- NH3(liq) / \ H CH3 trans-2-butene CH3CCCH3 H H \ / H2, Pd-C C = C syn- Lindlar catalyst / \ CH3 CH3 cis-2-butene docsity.com 2. Addition of X2 X X X | | | — C C— + X2  — C = C — + X2  — C — C — | | | X X X Br Br Br CH3CCH + Br2  CH3C=CH + Br2  CH3-C-CH Br Br Br docsity.com 3. Addition of hydrogen halides: H H X | | | — C C— + HX  — C = C — + HX  — C — C — | | | X H X a) HX = HI, HBr, HCl b) Markovnikov orientation Cl CH3CCH + HCl  CH3C=CH2 + HCl  CH3CCH3 Cl Cl docsity.com 5. As acids. terminal alkynes only! a) with active metals CH3CCH + Na  CH3CC -Na+ + ½ H2  b) with bases CH3CCH + CH3MgBr  CH4 + CH3C CMgBr SA SB WA WB docsity.com acid strength: CH4 < NH3 < HCCH < ROH < H2O < HF HC CH + NaOH  NR ( H2O = stronger acid! ) CH3CH2CCH + LiNH2  NH3 + CH3CH2CC -Li+ SA WA docsity.com 6. Ag+ terminal alkynes only! CH3CH2CCH + AgNO3  CH3CH2CC -Ag+  CH3CCCH3 + AgNO3  NR (not terminal) formation of a precipitate is a test for terminal alkynes. docsity.com Alkynes Nomenclature Syntheses 1. dehydrohalogenation of vicinal dihalide 2. coupling of metal acetylides with 1o/CH3X docsity.com Reactions, alkynes: 1. addition of H2 (reduction) 2. addition of X2 3. addition of HX 4. addition of H2O, H + 5. as acids 6. Ag+ 7. oxidation docsity.com