Exam 2 Flashcards
The abbreviation NAS stands for
Nucleophilic Aromatic Substitution
Meisenheimer Complex is formed addition-_______________ mechanism of ______ reaction.
elimination, NAS
Benzyne is formed in …………. aromatic substitution reaction.
nucleophilic
The state of hybridization of the triple bonded carbons in benzyne is…………….
sp2
Phenylation to 1,3-diketo compounds is an example of ……………………reaction.
NAS
Give an example with figure (in each case) of terminal alkene, internal alkene, and cycloalkene.
Write the structure of zingiberene, (R)- limonene and (S)- limonene.
In ethylene, the carbons are…………..hybridized.
sp2
Bromination of cis-2-butene produces a racemic mixture whereas trans-2-butene produces a meso compound-why?
Because halogen additions are determined by anti-addition and completely restricted rotation of the carbon-carbon bond of the halonium ion
Write the stability order of 1-butene, cis-2-butene, and trans-2-butene
1-butene < cis-2-butene < trans-2-butene
Write the chemical structure of DMSO.
What is Markovnikov’s rule?
Mark’s rule states that in the addition of (hydrogen halides) to an unsymmetrical alkene, the H atom adds to the more substituted carbon atom— that is the carbon that has the greater number of H atoms to begin with.
What is Anti-Markovnikov’s condition? Give an example
-a mechanism that avoids the carbocation intermediate
-the halogen adds to the less substituted carbon.
Ex: addition of hydrogen bromide to propene in the presence of benzoyl peroxide.
In the case of hydrohalogenation reaction………………..…..and ………………….….addition occur.
syn; anti
What do you mean by vicinal and germinal dihalides? Give example in both cases.
Vicinal: halides are next to each other
Geminal: relationship between 2 atoms or functional groups attached to same atom
Vicinal dihalide
when halogens are on adjacent carbons
Germinal dihalide
when both halogens are on the same carbon
What do you mean by halohydrin? How does it form?
A halohydrin is an organic molecule that contains both a halogen and an OH group.
Halo=halogen and Hydrin=OH.
AKA when a halogen and a hydroxyl are bonded to adjacent carbon atoms
How does a halohydrin form?
-Reaction Overview: the halohydrin formation reaction involves breaking a pi bond and creating a halohydrin in its place.
-by treatment of an alkene with a halogen X2 and H2O forms the halohydrin by addition of the elements X and OH to the double bond
What is NBS?
N-bromo succinimide is a useful reagent in organic chemistry
What purpose does NBS serve in organic synthesis?
(N-bromosuccinimide)
In H2O, NBS decomposes to form Br2, which then goes on to form a bromohydrin in aqueous DMSO by the same reaction mechanism as halohydrin formation
-In other words, Wohl-Ziegler reaction.
Hydroboration-Oxidation is an anti………………addition to alkenes.
Markovnikov
What is 9-BBN? Mention its use in organic synthesis.
9-boracicyclo[3.3.1] none or
9-BBN is a hydride-bridged primer, which cleaves in the presence of reducible substrates.
-This colorless solid is used in organic chemistry as a hydroboration reagent.
Mercurinium ion is formed in………………reaction.
oxymercuration
Oxymercuration-Demercuration is a ……………….hydration procedure.
indirect
What is the degree of unsaturation?
Degree of unsaturation is the number of pi bonds and/or rings in the molecule
Explain the degree of unsaturation considering C6H10 as an example.
-C6H10 has a degree of unsaturation of 2
-this means that C6H10 may contain 2 rings, 2 pi bonds, 1 ring and pi bond, or 1 triple bond
Hydrogenation is a ……………addition.
syn
Peroxyacetic acid is used in ………………reaction of alkenes.
epoxidation
When 2 substituents are added on the same side/face of a double bond
syn
When 2 substituents are added on opposite sides/faces of double bond
anti
Write the structures of E-3-methyl-2-pentene and Z-3-methyl-2-pentene.
?
Explain the terms syn and anti with appropriate examples.
Syn addition is the addition of two substituents to the same side of a double/triple bond, resulting in a decrease in bond order but an increase in number of substituents.
Generally the substrate will be an alkene or alkyne.
Anti addition: an addition reaction in which two substituents are added to opposite sides of a double bond.
…………..is an aliphatic peroxyacid whereas ………………is an aromatic peroxy acid.
peroxyacetic acid; m-chloroperbenzoic acid
Draw the orbital diagram of a secondary vinylic carbocation.
The product of the reaction between an alkene with HBr is………….whereas the product between the
reaction of an alkyne with HBr is…………..
an alkyl bromide; a vinyl bromide
What is keto-enol tautomerism? Give an example from nature.
Tautomers are isomers that can convert via migration of a proton, accompanied by a switch of a single bond and an adjacent double bond.
Ex: turmeric, as it contains curcumin as an active ingredient
What is Lindlar catalyst?
catalyst made from palladium on calcium carbonate that performs the hydrogenation of alkynes in the presence of H2
The hydrogenation of an alkyne with Lindlar catalyst produces…………..alkene whereas the treatment with Li/NH3 produces…………
cis alkene; trans alkene
Write the structure of a secondary vinylic carbocation.
Carbon dioxide is produced as a byproduct during oxidative cleavage of …………..alkynes.
terminal
Write the name of four strong oxidizing reagents.
O3-ozone
KMNO4-potassium permanganate
H2O2-hydrogen peroxide
HNO2-nitrous acid
Acetylide anion is formed on the treatment of…………………..with acetylene.
a strong anhydrous base
Isomeric compounds that rapidly interconvert by the movement of a ………………. are called………..
proton; tautomers
Treatment of an alkene with a halogen X2 and H2O forms …………………….
halohydrin
Nucleophilic aromatic substitution can occur when……………… groups are ortho or para to the halogen
atom.
strong electron withdrawing group
Nature produces ……….. alkene exclusively and Oils are derived from ……… having a larger number of
double bonds.
cis; fatty acids
The addition of HBr to an alkene generates ………………carbocation whereas …………..carbocation is
generated during the addition of HBr to an alkyne.
an alkyl secondary carbocation; a vinylic secondary carbocation
Which of the following compounds is least reactive towards NAS?
1-bromo-3-nitrobenzene
Formula for degree of unsaturation?
(2n+2) - x / 2
C44H64O2
Crocin
Translate this to form where degree of unsaturation can be calculated:
C6H5N
C6H4
Translate this to a form where degree of unsaturation can be calculated:
C6H5NO2
C8H12
Translate this to a form where degree of unsaturation can be calculated:
C9H16Br2
C9H18
Translate this to a form where degree of unsaturation can be calculated:
C10H12N2O3
C10H10
Translate this to a form where degree of unsaturation can be calculated:
C20H32ClN
C20H32
Translate this to a form where degree of unsaturation can be calculated:
C44H64O2+
C44H64
What are the basic differences between SNAr reaction with SN1 and SN2 reactions?
SN1/SN2 = alkyl halides
SNAr = dissociation & stable carbocation
SN2 = Nu back attacks as LG leaves
SNAr = flat ring so no back attack & no dissociation
addition-elimination = meisenheimer
elimination-addition = benzyne intermediate
Use chlorobenzene as an example for why SNAr reactions are not considered either SN1 or SN2
-chloronbenzene and SN1 not happen bc a positive charge is created on the ring;
-chlorobenzene is not an SN2 reaction bc steric hindrance is created.
SNAr will bc if strong EWG at ortho/para through addition elimination = Meisenheimer complex
What is benzyne?
intermediate formed in elimination-addition reaction; when there is no EWG
Why 2-chloropropane is formed as the sole product in the reaction between propene and HCl? Explain with mechanism.
propene is unsymmetrical to MKV rule = H-less substituent
Why secondary carbocation is more stable than primary carbocation? Explain the details.
Secondary carbocation has lower activation energy so a faster reaction & lower effect
Discuss the mechanism (drawing is essential) of the electrophilic addition of water to 1-methylcyclohexene.
hydration-electrophilic addition of water; pi bond attacks H3O+; electrophile added to pi bond; formed carbocation; Nu (H2O) attacks carbocation; water removes proton & forms alcohol; acid catalyzed
How TMBE can be synthesized from the electrophilic addition of alcohol to alkenes?
tert-butyl methyl ether; ELECTROPHILIC ADDITION; methanol and 2-dimethylpropene; catalyzed by H2SO4; MKV rule
Draw and explain the mechanism of bromination of cis-2-butene
halogenation; electrophile added to pi bond; breaks/forms 4 bonds = rate determining.; bridges bromonium ion; nucleophilic attacks ion; racemic mixture with cis bc added anti
Why is hydroboration regioselective? Explain the mechanism considering hydroboration-oxidtion reaction to propene.
steric factor & electronic/inductive effects; BH3 added to alkene, large group to less hindered & adjacent methyl stabilizes partial positive charge
Explain the stepwise mechanism of the reaction between mercury (II) acetate to ethylene.
mercury (II) acetate dissociates = +Hg(OAc); attacks pi bond and forms mercurinium ion; water approaches ion from anti to ring; MKV = water added to more substituted
What is ozonolysis? Explain with stepwise mechanism.
oxidative cleavage of alkene to carbonyl; pi and sigma bonds broken & replaced with C=O bonds; ozone has both nucleophilic and electrophilic capabilities
Explain with suitable examples the concept of E- and Z- alkenes. Is there any difference between cis/trans with E/Z? Justify your answer.
when 3 or 4 different groups use E/Z instead of cis/trans; visually split double bond and asses priority of each side
E = higher priority on opposite sides
Z = higher priority on same side
Cis-2-butene has a higher boiling point (40C) than trans-2-butene (10C) - explain
2 methyls on same side of cis form net dipole moment; polar = higher bp
How can you correlate the melting points of oleic acid, linoleic acid, and linolenic acids with their double bonds?
fatty acid w same number of C that increases in double bonds = mp decreases
What is mercurinium ion? When does it form?
it is a cyclic intermediate with + charge; results from + Hg(OAc) reacting with alkene; oxymercuration rxn
What is keto-enol tautomerism? Explain with the example of curcumin.
enols rearrange to form ketones through movement of proton from OH to alkene carbon; ketone more stable
Hydration of terminal alkynes in the presence of mercuric sulfate always yields a methyl ketone whereas hydration of internal alkynes produces mixture of ketones. Explain with appropriate example.
terminal = methyl ketone bc addition of water is MKV
Hydroboration-oxidation of an internal alkyne produces ketone whereas the same reaction for a terminal alkyne yields aldehyde-why? State the rule associated with this.
anti-MKV bc of the way H2O is added
Oxidation (KMnO4 or ozone) of unsymmetrical internal alkynes produces two carboxylic acids whereas under the same condition terminal alkyne produces one carboxylic acid. Explain
terminal alkynes oxidize and form carboxylic acid and CO2
Write the (i) reagents and (ii) mechanistic steps and (iii) explanation associated with the following reaction:
i.) 6-C alkyne, NaNH2, NH3, alkyl halide
ii.) produce hydrocarbon that leads to larger alkynes; acetylide anion reacts with alkyl halide; transition state until halide leaves; inversion of configuration since SN2
