ORG2 Final Preparations

38 flashcards · Physics · by John Mark Webb

(14) The 1,2 adduct is usually formed faster and is said to be the product of kinetic control. The 1,4 adduct is usually more stable and is said to be the product of thermodynamic control.
(14) Diels-Alder cycloaddition reactions require a diene and a dienophile.
(14) Any unsubstituted 1,3-diene cyclic diene gives the same product from 1,2- and 1,4-addition.
(14) Although an electron-withdrawing group will increase the reactivity of a dienophile, it will decrease the reactivity of a diene.
(14) The most reactive dienophiles contain electron-withdrawing groups.
(14) Notice that the triple bond keeps a double bond in the product.
(14) In general, the more conjugated double bonds that a molecule has, the longer the wavelength at which it will absorb UV light.
(14) The third and final step is ozonolysis.
(15) Hückel’s rule only allows for 6, 10, 14, Aromatic and anti-aromatic are both cyclic and conjugated. Aromatic compounds have 4n+2 pi electrons. Anti-aromatic compounds have 4n pi electrons. Non-aromatic just don't meet the criteria for either.
(15) When determining the dipole moment, you have to make sure that the two cyclic structures are aromatic according to the 4n+2 rule.
(15) The IR data can help determine the substitution pattern of the ring.
(16) The mechanism for the electrophilic bromination of benzene. The reaction occurs in two steps and involves a resonance stabilized carbocation intermediate.
(16) Mechanism for the Friedel–Crafts alkylation reaction of benzene with 5-chloropropane to yield isopropylbenzene (cumene). The electrophile is a carbocation, generated by AlCl3-assisted dissociation of an alkyl halide.
(16) Despite its utility, the Friedel–Crafts alkylation has several limitations. For one thing, only alkyl halides can be used. Another limitation is that Friedel–Crafts reactions don’t succeed on aromatic rings that are substituted either by a strongly electron-withdrawing group such as carbonyl (C=O) or by a basic amino group that can be protonated. A third limitation to the Friedel–Crafts alkylation is that it’s often difficult to stop the reaction after a single substitution. Once the first…
Limitation 1: Limitation 2: Limitation 3: Limitation 4:
(16) The three possible disubstituted products—ortho, meta, and para—are usually not formed in equal amounts. Instead, the nature of the substituent initially present on the benzene ring determines the position of the second substitution.
(16) Classification of substituent effects in electrophilic aromatic substitution. All activating groups are ortho- and para-directing, and all deactivating groups other than halogen are meta-directing. The halogens are unique in being deactivating but ortho- and para-directing.
(16) Carbocation intermediates in the nitration of toluene. Ortho and para intermediates are more stable than the meta intermediate because the positive charge is on a tertiary carbon rather than a secondary carbon.
(16) Carbocation intermediates in the nitration of phenol. The ortho and para intermediates are more stable than the meta intermediate because they have more resonance forms, including one particularly favorable form that involves electron donation from the oxygen atom. It it ortho and para because it likes the =+O–H intermediate.
(16) Carbocation intermediates in the nitration of chlorobenzene. The ortho and para intermediates are more stable than the meta intermediate because of electron donation of the halogen lone-pair electrons.
(16) Carbocation intermediates in the nitration of benzaldehyde. The ortho and para intermediates are less stable than the meta intermediate. The meta intermediate is more favorable than ortho and para intermediates because it has three favorable resonance forms rather than two.
(16) Mechanism of nucleophilic aromatic substitution. The reaction occurs in two steps and involves a resonance-stabilized carbanion intermediate.
(16) Summary of reactions!
(17) A stronger alcohol acid is less substituted. A stronger phenol acid will have a strong electron withdrawing group in its para position.
(17) Mechanism for the acid-catalyzed dehydration of a tertiary alcohol to yield an alkene. The process is an E1 reaction and involves a carbocation intermediate.
(17) Mechanism for the dehydration of secondary and tertiary alcohols by reaction with POCl3 in pyridine. The reaction is an E2 process.
(17) Mechanism for the formation of phenol by acid-catalyzed rearrangement of cumene hydroperoxide. This mechanism includes a proton shift.
(17) Cumene reacts with air at high temperature by benzylic oxidation through a radical mechanism to form cumene hydroperoxide, which is converted into phenol and acetone by treatment with acid. This is a particularly efficient process because two valuable chemicals are prepared at the same time.
(17) Summary of reactions!
(18) Base-catalyzed epoxide opening is a typical SN2 reaction in which attack of the nucleophile takes place at the less hindered epoxide carbon.
(18) Summary of reactions!
(19) Mechanism of imine formation by reaction of an aldehyde or ketone with a primary amine. The key step is the initial nucleophilic addition to yield a carbinolamine intermediate, which then loses water to give the imine. This is an imine:
(19) Mechanism for enamine formation by reaction of an aldehyde or ketone with a secondary amine, R2NH. The iminium ion intermediate formed in step 3 has no hydrogen attached to N and so must lose H+ from the carbon two atoms away.
(19) Mechanism for the Wolff–Kishner reduction of an aldehyde or ketone to yield an alkane.
(19) Mechanism of acid-catalyzed acetal formation by reaction of an aldehyde or ketone with an alcohol.
(19) Summary of reactions!
(20) As Table 20-4 shows, an electron-donating (activating) group such as methoxy decreases acidity by destabilizing the carboxylate anion, and an electron-withdrawing (deactivating) group such as nitro increases acidity by stabilizing the carboxylate anion.
(20) Mechanism for the basic hydrolysis of a nitrile to yield an amide, which is then hydrolyzed further to a carboxylic acid anion.
(20) Summary of reactions!