Addition Reactions Flashcards
The addition of water (H₂O) to an alkene in the presence of an acid catalyst, forming an alcohol
Acid-catalyzed hydration
The addition of a hydrogen halide (HX, where X = Cl, Br, I) to an alkene, forming an alkyl halide.
Hydrohalogenation
A two-step reaction sequence that achieves Markovnikov addition of water to an alkene without carbocation rearrangements.
Oxymercuration-demercuration
A two-step reaction sequence that achieves anti-Markovnikov addition of water to an alkene.
Hydroboration-oxidation
The addition of hydrogen (H₂) to an alkene in the presence of a metal catalyst (e.g., Pd, Pt, Ni), forming an alkane
Catalytic hydrogenation
The addition of a halogen (Cl₂, Br₂) to an alkene, forming a vicinal dihalide (two halogens on adjacent carbons).
Halogenation
The addition of a halogen and a hydroxyl group (OH) to an alkene, forming a halohydrin. This reaction occurs when the halogenation is carried out in the presence of water. The water molecule acts as a nucleophile and attacks the halonium ion, leading to the formation of a halohydrin.
Halohydrin formation
Typically exothermic (ΔH < 0) due to the formation of stronger sigma bonds from weaker pi bonds.
However, they often result in decreased entropy (ΔS < 0) as two molecules combine to form one.
Addition reactions
Typically endothermic (ΔH > 0) due to the breaking of strong sigma bonds to form weaker pi bonds.
However, they often result in increased entropy (ΔS > 0) as one molecule forms two.
Elimination reactions
_______________ predicts the regiochemistry of addition reactions to alkenes. It states that in the addition of a protic acid (HX) to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached, while the halide (X) will attach to the more substituted carbon.
This preference is due to the stability of the intermediate carbocation formed during the reaction. The more substituted carbocation is more stable due to hyperconjugation and inductive effects, leading to the observed regioselectivity.
Markovnikov’s Rule
_______________ describes the regiochemistry of addition reactions to alkenes, where the addition of a hydrogen atom (from a reagent like HBr) occurs at the more substituted carbon of the double bond, and the other atom (e.g., Br) attaches to the less substituted carbon. This is in contrast to the typical Markovnikov addition, where the hydrogen adds to the less substituted carbon.
anti-Markovnikov rule
The addition of two hydroxyl groups (OH) to an alkene with anti stereochemistry, forming a diol (a compound with two alcohol groups).
Anti-dihydroxylation
epoxidation
The addition of two hydroxyl groups (OH) to an alkene with syn stereochemistry, forming a diol.
Syn-dihydroxylation
formation of a cyclic osmate ester
The cleavage of a carbon-carbon double bond by an oxidizing agent, forming two carbonyl compounds (aldehydes or ketones).
Ozonolysis
(oxidative cleavage)
Hydrohalogenation
Hydration acid catalyzed
Oxymercuration-demercuration
- anti addition only
Hydroboration-oxidation
Catalytic Hydrogenation
Halogenation
Halohydrin Formation
Syn dihydroxylation
Ozonolysis
Anti dihydroxylation
epoxidation
anti addition
Markovnikov or Anti-Markovnikov?
Hydroboration
Anti-Markovnikov
Markovnikov or Anti-Markovnikov?
Oxymercuration
Markovnikov
Markovnikov or Anti-Markovnikov?
Hydration acid catalyzed
Markovnikov
Markovnikov or Anti-Markovnikov?
Hydrohalogenation (HX)
Markovnikov
Markovnikov or Anti-Markovnikov?
Halohydrin Formation
Markovnikov
Syn of Anti Addition ONLY?
Hydroboration
Syn
Syn of Anti Addition ONLY?
Halogenation
Anti
- due to bridged halonium ion mechanism and other halide backside attack
Syn of Anti Addition ONLY?
Halohydrin Formation
Anti
Syn of Anti Addition ONLY?
Dihydroxylation w OsO4 or KMnO4
Syn
Syn of Anti Addition ONLY?
Dihydrozxylation via epoxidation
Anti
Syn of Anti Addition ONLY?
Catalytic Hydrogenation
Syn
Examples of _______________
MMPP
mCPBA
Peracetic Acid (PAA)
Peroxy Acids
used as epoxides
Hydration with acid can be accompanied by rearrangements if a more stable carbocation intermediate can be formed through a hydride or alkyl shift. To avoid this, _____________ of alkenes is an alternative that does not give rearrangement.
oxymercuration
Anti-Markovnikov ALCOHOLS can be obtained through ________________
hydroboration
When alkenes (olefins) are treated with strong aqueous acid (H3O+) they undergo net addition of ______ across the double bond (“hydration”)
water
For acid catalyzed hydration reactions:
Acids like H2SO4 are used since the conjugate base, HSO4(-), is a poor __________ and will not compete with H2O in attack on the carbocation
nucleophile
- if HCl is used then Cl- competes
H2O will not add to alkenes by itself, however a __________ is required.
strong acid
A ___________ reaction is one that shows a strong preference for the formation of one constitutional isomer (“regioisomer”) over another.
regioselective
Useful mnemonic for Markovnikov is …….
“the rich (in C-H bonds) get richer (get another C-H bond)”
Treatment of alkenes with mercury (II) salts and water leads to the addition of water and mercury across the C-C pi bond. This is called _____________
oxymercuration
Oxymercuration-demercuration:
The reaction proceeds through attack of the nucleophile on a 3-membered intermediate known as an oxymercurinium ion, which resembles the halonium ion intermediate in reactions such as halogenation of alkenes. As like in halogenation, addition occurs to give the products of ___(anti or syn)___ addition
anti
In the demercuration step, mercury is removed by treating the product with ____________ , giving the alcohol.
sodium borohydride (NaBH4)
When an alkene is treated with a mercury(II) salt such as mercuric acetate [Hg(OAc)2] or mercuric trifluoroacetate Hg(OCOCF3)2 in the presence of H2O, addition occurs across the C-C pi bond, resulting in a new C-OH bond and a C-Hg bond. This reaction is called _____________
oxymercuration.
Organomercury compounds tend to be highly _________ and it is best to avoid handling them if at all possible
toxic
2 commonly used reagents used in oxymercuration
- ____________
- ____________
In the demercuration step, treatment with _______________ replaces C-Hg with C-H, resulting in the alcohol and a little pool of elemental liquid mercury that accumulates at the bottom of the flask.
sodium borohydride (NaBH4)
Oxymercuration is also regioselective for the “______________” alcohol products!
Markovnikov
- The selectivity seems to be very good – one study found only about a 1% yield of the minor anti-Markovnikov alcohol product!!!!!
The Mechanism of Oxymercuration Goes Through A 3-Membered “________________”
Mercurinium Ion
- similar to bridged halonium ion of Br & Cl
True or False:
Oxymercuration Provides Markovnikov Alcohols Without Rearrangement
True
____________is an addition reaction between an alkene (olefin) and a a borane (neutral species containing a B-H bond). A C-C pi bond is broken, and a C-H bond as well as a C-B bond is formed.
Hydroboration-oxidation
Oxidation of the resulting organoborane with _______________ then replaces the C-B bond with a C-OH bond.
hydrogen peroxide (H2O2)
Hydroboration is stereoselective for_____ addition
syn addition
that is,the H and B are delivered to the same face of the alkene. Oxidation of the C-B bond occurs with complete retention of stereochemistry.
Each equivalent of BH3 is capable of performing ____ alkene hydroboration reactions
3
- one for each B-H bond
The transition state of hydroboration oxidation reaction is ______________
concerted (all at once)
m-CPBA (meta-chloroperoxybenzoic acid) is a useful reagent for the formation of___________ from alkenes
epoxides
Epoxides are 3-membered cyclic ethers. Since the inner bond angles of epoxides (approximately 60°) deviate significantly from the preferred tetrahedral geometry around carbon (109.5°) , they possess considerable__________ and undergo a large number of useful ring-opening reactions with nucleophiles
ring strain
Syn-dihydroxylation of alkenes with OsO4 is functionally equivalent to dihydroxylation with cold, basic ____________
KMnO4
- but OsO4 is better
__________is a useful reagent for the syn-dihydroxylation of alkenes
Osmium tetroxide (OsO4)
Alkenes (and alkynes) will undergo addition of hydrogen (H2) in the presence of a __________
metal catalyst
- These metals are typically finely divided and adsorbed on the surface of a high surface-area material such as activated carbon (most common) or alumina (Al2O3) , hence Pd/C, Pt/C, Rh/Al2O3 and so on. Since these do not dissolve in solution they are called heterogeneous catalysts
Since addition results in a new C-H bond at the expense of a C-C bond the oxidation state of carbon decreases. These reactions are commonly referred to as ___________
reductions
Catalytic Hydrogenation rxn
In this reaction a C-C pi bond and a H-H bond are broken, and two C-H sigma bonds are formed, making it ____________
exothermic
- despite the significantly greater stability of the products, no reaction between the alkene and H2 typically occurs in the absence of the metal
True or False
Alkynes are even more reactive towards hydrogenation than alkenes, and can typically be reduced to alkenes without affecting the other alkenes in the molecule.
True
Alkenes undergo halogenation when treated with Cl2 & Br2 to give ___________
vicinal dihalides
Halogenation reactions are stereoselective and give _______ addition products
anti addition
Halogenation mechanism:
proceeds through a __________________ which undergoes backside attack at carbon by a nucleophile to give the anti-addition product
cyclic halonium ion
The terms syn– and anti– refer to the dihedral angle observed between the two C-halogen bonds when we look directly along the C-C bond. We say this addition is anti– because the dihedral angle between the two C-halogen bonds is _______ & syn is _________
180°
0°
Halogenation rxn:
Although a halonium ion has a positive formal charge on the halogen, it’s actually the carbons that are _______________. This is easier to recognize if you remember that halogens are more electronegative than carbon, so the carbon-halogen bonds will have partial positive character on carbon. That’s why it’s called, “formal” charge
electrophilic
One difference between halogenation and halohydrin formation is that the two new sigma bonds are formed to non-identical atoms (oxygen and halogen), which gives rise to the possibility of forming a mixture of _________________
constitutional isomers
When bromination/chlorination of alkenes is carried out in the presence of water (often as a co-solvent),____________ products are formed
halohydrin
C-OH
C-X
Adding 2 equivalents of HCl or HBr in an Alkyne Hydrohalogenation reaction results in a ______________
geminal dihalide
