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使用内层均减电剂,与烯化物交叉电友合N-甲胺

  • 0Department of Chemistry, UW-Madison, Madison, Wisconsin 53706, United States.

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Electrophilic 1,2- and 1,4-Addition of X<sub data-lazy-src=

3.4K

Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.

Conjugated dienes react with halogens in a similar manner. However, in addition to the 1,2-dihalide, they also form a 1,4-dihalide. The mechanism involves two steps.
First, a nucleophilic attack by one of the diene π bonds on the electrophilic center of the polarized halogen molecule forms a halonium ion intermediate. This is followed by a nucleophilic attack of the...

Nucleophilic Aromatic Substitution: Elimination–Addition 01:11

5.0K

Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...

Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene 01:17

7.6K

The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.

With conjugated systems like 1,3-butadiene, the addition of one equivalent of HBr yields a mixture of products: 1,2 and 1,4-addition products. As shown below, the mechanism involves the addition of H+ across one of the double bonds of the conjugated diene to form a resonance stabilized allyl cation. This is followed by the nucleophilic attack of...

Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene 01:13

7.3K

Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.

Unlike fluorine, iodine is highly unreactive for...

Radical Substitution: Allylic Bromination 01:27

6.4K

In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...

α-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview 01:19

3.2K

The pinacol and McMurry reactions involve the reductive coupling of ketones or aldehydes. Similarly, the bimolecular reductive coupling of two ester molecules in the presence of sodium metal in an aprotic solvent yields an α-hydroxy ketone product. The α-hydroxy ketone is also called acyloin, so the reaction is referred to as ‘acyloin condensation.’

In the acyloin condensation reaction, esters are converted to ketyls, which undergo radical dimerization to form an unstable tetrahedral...