Organic Chemistry - Addition Reactions of Alkenes and Alkynes

HX

Hydrohalogenation, Markovnikov addition of H and X across the alkene, SYN AND ANTI, only useful when carbocation rearrangement does not occur

HBr, ROOR

Hydrobromination, Treatment with an alkene gives an anti-Markovnikov addition of H and Br across the alkene

H2SO4, H2O (Bascially H3O +)

Acid-cat. Hydration, Treatment with an alkene gives a Markovnikov addition, SYN AND ANTI

1) Hg(OAc)2, H2O

2) NaBH4

Oxymercuration-demurcuration, treatment with an alkene gives an Markovnikov addition of H and OH across the alkene, WITHOUT CARBOCATIONS, ANTI

1)BH3 x THF

2) H2O2, NaOH

Hydroboration-oxidation, Treatment with an alkene gives an anti-Markovnikov addition of H and OH across the alkene, a SYN ADDITION

H2, Pt

Hydrogenation, Treatment with an alkene gives a SYN ADDITION of and H and H across the alkene

X2, CH2Cl2

Halogenation, treatment of an alkene gives an ANTI addition of Br and Br across the alkene

X2, H2O

Halohydrin Formation, treatment of an alkene gives ANTI addition of Br and HO, OH AT MORE SUBSTITUTED POSITION

1) RCO3H

2) H3O +

1)MCPBA

2) H3O+

•First step is SYN

•Anti Dihydroxylation, treatment of an alkene with a proxy acid (RCO3H) converts the alkene into an epoxide

•which is then opened upon treatment with aqueous acid to give a trans-diol

KMnO4, NaOH, cold

Syn Dihydroxylation, Treatment with an alkene gives a syn addition of OH and OH across the alkene

1) OsO4

2) NaHSO3, H2O

Syn Dihydroxylation, Treatment with an alkene gives a syn addition of OH and OH across the alkene

1) O3

2) DMS

1) KMnO4

2) H3O+

Ozonolysis, Ozonolysis of an alkene causes cleavage of the C=C bond, giving two compounds, each of which possesses a C=O bond

Nucleophile Only (7)

Cl, Br, I, HS, RS, H2S, RSH

Base (only) (2)

DMN, DBU

Strong Nuc/ Strong base (4)

HO, MeO, EtO, (CH3)3O

Weak Nuc/Weak Base (3)

H2O, MeOH, EtOH

More stable? Cis or trans?

Trans

E2 Mechanism

•rate = k [substrate] [base]

•occurs rapidly at tertiary base bc it can act as an base

•Regiochemistry: can produce more than one product (major and minor) more substituted, more likely to occur, effected by the base that is used

•Stereoselectivity: regiochemistry is not an issue when the same result will occur matter where the double bond is, both cis and trans are made but trans predominates

•Stereospecificity: when there is only one proton, draw newman projection

E1 Mechanism

•tertiary more reactive than primary

•regioselectivity: more substituted product is the major product (regardless of base used)

•stereoselectivity: also prefer trans like E2

•Stereospecificity: not stereospecific

If there is an OH group on the molecule (good or bad leaving group) ...

it is a terrible leaving group, and it needs to be protonated first so that it can leave (acid catalyzed hydration reaction)

Possible outcomes for Reagents

Review pg. 389 in Klein

With a strong base....

(NaOMe) the product is more substituted

With a strong, hindered base...

(t-BuOK) the product is at the least substituted

CHCl3 (KOH)

•Dicholocarbene addition, cyclopropane SYN

•Because KOH is present we also show the 2 chlorine at the top of the carbene

CH2I2 (Zn(Cu))

Simmons-Smith reaction, cyclopropane SYN

H3O+ (H2SO4, H2O)

OH at most substituted place, Markinkov, SYN and ANTI

HIO4/H2O

cleavage of 1,2-diols

Saturated Fat

•no double bonds •higher melting point

Unsaturated Fat

•double bond (there is a kink) •lower melting point

Bases that will depronate a terminal alkyne

NH3, H2, C2H2

1) excess NaNH2

2) H2O

Elimination, a vicinal or geminal dibromide is converted to an alkyne

•H2, Pt (high pressure)

•H2 / Lindlar's Catalyst

Catalytic Hydrogenation for Alkynes

•Lindlar's Catalyst makes an alkyne turn into a cis-alkene

•H2, Pt: alkyne converted to alkane

Dissolving Metal Reduction

Na, NH3, (l)

MAKES TRANS: first Na gives an E-, then NH3 takes the pair of E- and replaces it with an H, and then again the Na gives an E- to the radical and then again NH3 takes the E- pair. (left with a double bond in the final product, from a triple bond, protons are in trans position)

Hydrohalogenation of Alkynes, HX

•Markovnikov addition when Alkynes are treated with HX (can have X at a vinyl position), also there are two additions of HX to get a dihalide

•rate = K [alkyne][HX]^2

Radical addition of HBr to Alkynes

radical addition only occurs with HBr and not HCl or HI, anti-markovnikov, produces trans and cis

to go from a dihalide to a alkyne you use...

1) NaNH2/NH3

2) Or you can eliminate the halogens

to go from alkyne to a dihalide you use...

Excess HX

•H2SO4, H2O, HgSO4

Acid-Catalyzed Hydration of Alkynes

•Markovnikov addition, hydroxyl at more substituted, ENOL TURNS INTO KETONE.

•can have a mixtrue of ketones if original molecule is unsymmetrical (but this is useless)

•regiocehmisty controlled by base used

-H2SO4, H2O / HgSO4 OH at (most substituted

Hydroboration-Oxidation of Alkynes

1) R2BH / H2O2, NaOH

1) Proton Transfer 2) Proton Transfer, makes an aldehyde at the end

•Reagents: Disiamylborane, 9-BBN

Halogenation of Alkynes

•X2

• excess X2 - no double or triple bonds

• X2 (one equivalent) - ANTI addition (there are major and minor products)

Ozonolysis of an Alkyne

•1) O3

2) H2O

•when ozone is followed by water, there is an OH added to the cleavage

•if there is a terminal side it is converted into CO2

Alkylation of Terminal Alkynes

•an alkyl group is installed on the terminal alkyne