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Mechanisms
Organic Chemistry
Question | Answer |
---|---|
Define Hydrogenation | addition of H2 to a multiple bond |
Hydrogenation | alkene to alkane |
Notes on Hydrogenation | syn addition |
H2/Pd, Pt, or Ni | Hydrogenation |
How does heat affect stability? | less heat = more stable more heat = less stable |
Syn Addition | two atoms or groups add to the same face of a double bond |
Anti Addition | atoms or groups add to opposite faces of the double bond |
Stereoselectivity | a reaction in which a single starting material can give two or more stereoisomeric products but yields one of them in greater amounts than the other |
slowest to fastest rate of addition | HF<<HCL<HBR<HI |
weakest acid to strongest acid HI, HF, HCL, HBR | HF<<HCL<HBR<HI |
Markovnikov's Rule | when an unsymmetrically substituted alkene reacts with a hydrogen halide, the hydrogen adds to the carbon that has the greater number o fhydrogesn, and the halogen adds to the carbon having fewer hydrogens |
Name the mechanism and any rule that applies: CH3CH2CH=CH2 + HBR <acetic acid> CH3CH2CH(BR)CH3 | Hydrohalogenation and markovnikov's rule |
Define Hydrohalogenation | is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes |
Hydrohalogenation | Alkene to alkyl halide Alkyne to Alkenyl Halide Alkyne to Geminal dihalide |
Notes on Hydrohalogenation | Markovnikov's Rule |
Hydrogen Halide ex: HBR, HCL | Hydrohalogenation |
Define Dehydration | loss of water |
Dehydration | alcohol to alkene |
What kind of mechanism does Dehydration take place | E1-carbocation E2-no carbocation |
H2SO4 or H3PO4 | Dehydration |
Elimination 1 | alcohol to alkene carbocation present H2SO4 or H3PO4 TERTIARY weak NU, weak base (NH3/CH3NH2/C5H5N or pyridine), heat SECONDARY heat, weak base, weak NU, good LG, steric hindrance |
Elimination 2 | alcohol to alkene no carbocation H2SO4 or H3PO4 PRIMARY strong bulky base sterically hindered SECONDARY strong base sterically hindered secondary LG |
SN2 | nucleophillic substitution chirality present=stereochem achiral present=no stereochem PRIMARY aprotic solvent,good NU,strong/weak base, unhindered SECONDARY aprotic solvent, good NU, unhindered, inversion, backside attack), no carbocation |
SN1 | carbocation forms enantiomers TERTIARY protic solvent, good NU, forms enantiomers SECONDARY protic solvent, good NU, |
Very Good NU | I, HS, RS |
Good NU | Br, OH, RO, CN, N3 |
fair NU | NH3, Cl, F, RCO2 |
Weak NU | H20, ROH |
Very Weak NU | RCO2H |
Aprotic Solvents examples | no hydrogen bonding; no acidic hydrogen; stabilize ions; favor SN2 EXAMPLES DCM, THF, ethyl acetate, acetone, DMF, MeCN or acetonitrile, DMSN or dimethyl sulfoxide, |
Protic Solvents examples | hydrogen bonding; acidic hydrogen; cations and anions;favor SN1 EXAMPLES Formic acid, n-Butanol, isopropanol, ethanol, methanol, acetic acid, water |
Primary | SN2 E2 |
Tertiary | SN1 E1 |
Secondary | all four |
alkyl halide/AgNO3/aq. EtOH | SN1 |
Alkyl Halide/NaI/acetone | SN2 |
Alcohol/HX | SN1 |
alcohol/SOCl2 or PX3 | SN2 |
alkyl halide/H2O | E1 |
alkyl halide/KOH/heat | E2 |
alcohol/H2SO4/heat | E1 |
Dehydrohalogenation | alkyl halide to alkene |
What kind of mechanism is Dehydrohalogenation | E2 |
Strong Base | Dehydrohalogenation of E2 |
Free Radical Addition of HBR | Alkene to Alkyl Bromide |
Notes on Free Radical Addition | Anti-Mark peroxides needed |
HBR, Peroxides | Free Radical Addition of HBR |
Hydration | Alkene to alcohol Alkyne to ketone |
Notes on Hydration | Markovnikov's |
dilute H2SO4, H20 | Hydration |
Hydroboration-oxidation | Alkene to alcohol |
Notes on Hydroboration-oxidation | Syn addition, anti-mark |
1.B2H6, diglyme/2.H2O2, OH | Hydroboration-oxidation |
Halogenation | Alkene to vicinal dihalide alkene to vicinal halohydrin alkyne to vicinal dihalide-trans alkene alkyne to tetrahalide |
Notes on Halogenation | anti addition, OH adds to more substituted Carbon |
X2, CHCL3, or CCl4 | Halogenation |
X2, H2O | Halogenation alkene to vicinal halohydrin |
Epoxidation | Alkene to epoxide (carboxylic acid) |
Notes on Epoxidation | Syn addition |
peroxy acid | Epoxidation |
Ozonolysis | Alkene to aldehydes or ketones alkyne to 2 carboxylic acids |
Notes on Ozonolysis | Ozonide is intermediate |
1. O3/ 2. H2O, Zn or (CH3)2S | Ozonolysis |
Formation of alkyl tosylate | alcohol to alkyl tosylate |
Notes on alkyl tosylate | -OTs is leaving group |
Tosylate chloride | Alkyl Tosylate |
Formation of Alkyne Anion | Terminal Alkyne to Alkyne anion (conj. base) Na, NH3 |
NaNH2, NH3 | Alkyne Anion |
Alkylation | Alkyne anion to alkyne |
Notes on Alkylation | Alkyne anion is LG |
Methyl or primary alkyl halide | Alkylation |
Formation of Alkyne | Vicinal dihalide to alkyne |
Notes of formation of alkyne | double dehydro-halogenation |
1. 2NaNH2, NH3/ 2. H2O | Formation of alkyne |
Hydrogenation of Alkynes | alkyne to alkane |
2H2/Pt, Pd, or Ni | Hydrogenation of Alkynes alkyne to alkane |
Lindlar Reduction | alkyne to cis alkene |
Notes on Lindlar Reduction | Syn Addition |
H2/CaCO3 | Lindlar Reduction |
Metal Ammonia Reduction | alkyne to trans alkene |
Notes on Metal Ammonia Reduction | free radical intermediates |
Na or Li/NH3 | alkyne to trans alkene |
X2 | Alkyne to vicinal dihalide-trans alkene;halogenation |
2X2 | Alkyne to tetrahalide/halogenation |
HX | alkyne to alkenyl halide;hydrohalogenation |
2HX | Alkyne to geminal dihalide;hydrohalogenation |
1. H20/ 2. H2SO4, HgSO4 (HgO) | alkyne to Ketone;hydration |
1. O3/ 2. H2O | Alkyne to 2 Carboxylic Acids;ozonolysis |