CHMB42H3 Lecture Notes - Lecture 6: Phenyl Group, Acetyl Group, Aniline

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17 Aug 2016

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Electrophilic aromatic substitution reactions: halogenation, nitration, sulfonation, friedel-crafts acylation: (rc=o) sub. Vinylic halides and ary halides carbocations are unstable no rearrangement. Product contains a c=o group, that can complex, f/c acylations must be carried out with more than one equivalent of alcl3: water is added. Formyl cl is unstable & must be generated in situ. Gatterman koch uses high p of co and hcl formyl cl & alcl3-cucl catalyst: friedel-crafts alkylation: (r) sub. Carbocation rearrangement to most stable carbocation (hydride shift/methyl shift) Straight-chain alkyl group can be placed on a benzene ring by means of friedel-crafts acylation, followed by reduction of the carbonyl group to methylene. Do not have to use large excess of benzene. 19. 12 how some substituents on a benzene ring can be chemically changed. 19. 14 the effect of substituents on reactivity. The slow step of an eas rxn is the addition of an electrophile to the nucleophilic aromatic ring to form a carbocation intermediate.

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1. Of Huckel's requirements for aromaticity, only this one is NOT required in the case of some compounds to be considered aromatic? 8. Which sequence of reagents would produce b) The system must be monocyclic. c) There must be (4n + 2) Ï electrons. d) The Huckel number of electrons must be completely 2. Zn(Hg), conc. HC delocalized. 2. 4-amino-2-chlorobenzaldehyde is NOz H2N NO2 3. Which of the following compounds are aromatic? Hint: 9. Refer to the following list of possible answers: So ) halogen h) RC-O D diazonium ion a. What group weakly activates benzene to b. What group slightly deactivates benzene to SeAr because a) I and II only c)I, II and â ¢ b) II and III only d) I and IlI only SAr by a +I e-donor inductive effect? of its-I withdrawal inductive effect, but is an ortho-/para- director because of its +R resonance e-donor 4. Which one of the following compounds is anti-aromatie? c. What group inhibits Friedel-Crafts alkylation and acylation d. What species is the electrophile e. What species is formed when but strongly activates a halo benzene to S&Ar because of its strong -R e-withdrawal resonance effect? In which case is the indicated unshared pair of electrons Nora contributor to the Ï aromatic system? 5. in Friedel-Crafts acylation? aniline reacts with NaNO HCVS? 10. Arrange these benzene compounds in order of decreasing (fastest to slowest) SeAr reactivity: . Cyclopentadiene is unusually acidic for a hydrocarbon a) The carbon atoms are all sp hybridized. b) Cyclopentadiene is aromatic. c) Removal of a proton from cyclopentadiene yields an a) III > IV > 11 > 1 c) IV I> III d) IV > â ¡ > I> aromatic anion. d) Removal of a hydride ion from cyclopentadiene What might be predicted to happen when the following substance undergoes Friedel-Crafts acylation? produces an aromatic cation. 11. Recalling that benzene has a resonance energy of 152 k mol and naphthalene has a resonance energy of 255 k mol', predict the two positions which would be occupied by bromine when phenanthrene (below) undergoes addition of Brã (circle two numbers). a) Substitution occurs in ring A, o- to the methylene gro b) Substitution occurs in ring A, o-to the nitro group. c) Substitution occurs in ring A, m- to the methylene g d) Substitution occurs in ring B, o-/p- to the methylene e) Substitution occurs in ring B, m. to the methylene 10 9

CHMB42H3 Lecture Notes - Lecture 6: Phenyl Group, Acetyl Group, Aniline

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