chem3331-bean-09 - {SQGLKU‘ cfié‘ffiér’b: Alkynes...

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Unformatted text preview: {SQGLKU‘ cfié‘ffiér’b: Alkynes (omit 9 - 6B) \' filo Structure: compare to alkene and alkane H H\ / H \ / H H \\\\)C — 0‘11”; H H H H H BDE of triple bond = BDE of double bond = BDE of 0-0 bond = BDE of first 7: bond: BDE of second a: bond: Percent 3 character/ Importance: sp hybrid orbital - sp2 hybrid orbital - sp3 hybrid orbital - Physical Properties: Since nonpolar compounds - similar to the alkanes/alkenes of corresponding molecular mass CommorLNames: Acetylenes HCECH terminal alkyne: CH3CH2_ CEO _H internal alkyne: CH3- C_=_C-CH3 1. Choose longest chain that contains the triple bond. Suffix is "yne" (or diyne,triyne, etc.) Triple bonds gets priority when it is the only functional group present. 9H3 H30 —C I CH3 2. Compounds with double and triple bonds in the longest chain are called "enynes." Numbering an enyne begins with the end that gives the multiple bonds the lowest possible numbers (double or triple may have the lower number). 9H3 HC -=- C-CHz-CH-(IJH-CHQ-CH= CH-CH3 CH3 If the numbering is the same from either direction, the double bond has priority and receives the lower number. HC E C'CHQ-CHz-CH = CH2 3. If the triple bond is not part of the parent name, name as an allgmyl side chain. 0/ C'CH3 4. Cyclic alkynes (ring size of at least 8 carbons necessary): Triple bond is understood to be between carbons 1 and 2. -0 Note: True bond angle of sp carbon is not reflected in the structure above! ALKYNE ACIDITY Compare the pKa values of hydrocarbons: H\ ,H H—CEC—H /C=C\ H30-H l' H+ H H [_ H+ l- e H CE e H H3oe ZC= H \H other pKa values: H2804 CH3C02H H20 CH3CH20H FORMATION OF ACETYLIDE ANIONS: Strong bases such as NaNH2, organolithium reagents, and Grignard reagents can deprotonate a terminal alkyne to form an acetylide anion. (Hydroxide is NOT strong enough.) C? R-CEC—H + r52 :NH2 —-————» e R-CEC—H + @QH —» Reactions of Acetylide Anions: A. Alkylation of the acetylide anion - a substituton reaction (8N2) 9 @ 'fi R—CEC: Na + R'—o—X fi—p H Examples: 1.NaNH2 CHacHg—CEC—H K. 2. CchH2 ' CH2 -Br 1.NaNH2 CHaCHQ—CEC—H K» 2. CH3C')H—CH3 Br B. Addition to carbonyl groups (aldehydes and ketones): G (9 FR R—CEC: Na + /C=O fi—p R Exam Ie: p 0 CH3 II I e (9 CH3C‘CH3 CHacH—CEC: Na x—p 2. H30+ Synthesis of Alkynes: Dehydrohalogenation of vicinal and geminal dihalides H H H R R_ g;_'(;_R Base \ / Base -—> 0= C ——> R-C= C-R | I / \ heat — x x R x x H X R ' ' Base \ / R—C—C—R _* C=C Base R-CEC-R | | / \ heat x H R H CH3- CIJH—CH- CHZCHg I Br Br H-C E c-<:H2c3H2c:H3 H-C E 00 HQCHQC H3 cHz—CH— CH20H2CH3 Br Br + NaNH KOH + 150°C Elir 200°C CH3' ('2— CH2 CH20H3 Br CH3-C E C'CH20H3 CH3-C E C-CHQCHa Bf' CH20H2CH3 Br Base Catalyzed Rearrangement of Alkynes H l G R—C—CEC—R' + B: I H H 9/ H_B + R— CEC—C \R, R— CEC—C—R' + Be: 11 £0 REACTIONS OF ALKYNES 1. Addition of H2 A. Catalytic Reduction (Hydrogenation) l. Reactive catalysts: H2 R — C E C— R ‘9 Pt, Pd, or Ni 2. Lindlar's catalyst: H2 / Pd(BaSO4) R—CEC—R a quinoline B. Dissolving Metal Reduction Li/NH l R—CEC—R ‘30» Mechanism: Lio R\ R—CEC—R ——> C Reactions of Alkynes (continued): II. Addition of H - X (HCI, HBr, Hl): X H I I R-CEC-H ZfiHX» R—C—C—H X H l H-X THX addition of HBr/peroxide: 'i i" R-CEC-H R—C—C—H peroxude l I H Br Ill. Addition of X2 (BI’2 or Clg) : R-CEC-R Xfizp C=C R-C EC-H % v #2 , .,. / 'C = C—cfl3 / H 2° (lbw/fg Caréccyfion fiah'hdion ‘7 a rue-Hy) area’s IV. Addition of H-OH (Hydration) A. Mercuric lon - catalyzed hydration: HO /H + R'CEC'H H20! \C=C H W R/ \H ‘— tautomers: special constitutional isomers that are interconvertible by a rapid EQ H-O\ /H H+ 0% ll" C=C C— —H / \ | R H V— R/ H Mechanism: H - H I - H H92+ $042 + / H20 H-Oj- /H H20 H O\ — / R-CEC-H ———> R—C=C —> 0:0 —> C—C Hg+ R R Hg+ o\\ 1 H20 H 0\\ l H o\ ' H6Hz \Czc/ C—C—H C—C—H <——> C_C_H «— \ I _’ / l / + l R/ H R H R H R H Examples: CHsCHe-CEc-H W, CHaCHg-CEC-CHa W, lo Addition of H-OH to alkynes (continued) B. Hydroboration/oxidation (non-Mark) - first step similar to addition of borane to alkene, but must use a hindered borane to prevent double addition: R H H BH BH ITHF , 2 R-C—=—C-H —3—» \C=C/ ME» R—é—C—H / \ i l H BH2 H BH2 Reagent used: B-H = SiazBH (disiamylborane) Sia BH R\ /H - R\ /H CH) R-CEC-H -—2——, 0:0 ML C20 —-> RCH2_0-H H BSia2 H/ OH O 1. Sia BH u EX CH -CEC-H A - - 3 2. H202/OH' CH3CH2 C H H20/H2804/HQSO4 S? CH3-C-CH3 V. ' ’ : Oxrdation of alkynes OH OH O O _ KMnO4A-i20 ' l - 2 H2O u n HO OH KMnO4A-i20 $2 ("3 H+ o o . I - E - g» u u 2 Strong OH-/heat R-C\ -+- [C‘R —_> R_C\ + Ic_R O 0 OH HO 1.03 2. H20 0 0 II II Fi-C\ + C~R OH HO . . 1.0 II . . . ittermmal: R-CEC-H THEE?» R—C + CO2 (Similar result With KMnO4) ...
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This note was uploaded on 11/09/2010 for the course CHEM 2324 taught by Professor None during the Spring '10 term at Lone Star College.

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chem3331-bean-09 - {SQGLKU‘ cfié‘ffiér’b: Alkynes...

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