Cyclohexadienyl

Benzene anion radical Methanol Cyclohexadienyl radical Methoxide ion... [Pg.440]

Step 3 The cyclohexadienyl radical produced m step 2 is converted to an anion by electron transfer from sodium H H... [Pg.440]

Cyclohexadienyl radical Sodium Cyclohexadienyl anion Sodium ion... [Pg.440]

The carbocation formed m this step is a cyclohexadienyl cation Other commonly used terms include arenium ion and a complex It is an allylic carbocation and is stabilized by electron delocalization which can be represented by resonance... [Pg.474]

When a molecular orbital method was used to calculate the charge distribution in cyclohexadienyl cation it gave the results indicated How does the charge at each carbon compare with that deduced by examining the res onance structures for cyclohexadienyl cation ... [Pg.475]

Most of the resonance stabilization of benzene is lost when it is converted to the cyclohexadienyl cation intermediate In spite of being allylic a cyclohexadienyl cation IS not aromatic and possesses only a fraction of the resonance stabilization of benzene... [Pg.475]

If the Lewis base ( Y ) had acted as a nucleophile and bonded to carbon the prod uct would have been a nonaromatic cyclohexadiene derivative Addition and substitution products arise by alternative reaction paths of a cyclohexadienyl cation Substitution occurs preferentially because there is a substantial driving force favoring rearomatization Figure 12 1 is a potential energy diagram describing the general mechanism of electrophilic aromatic substitution For electrophilic aromatic substitution reactions to... [Pg.476]

Figure 12 3 adapts the general mechanism of electrophilic aromatic substitution to the nitration of benzene The first step is rate determining m it benzene reacts with nitro mum ion to give the cyclohexadienyl cation intermediate In the second step the aro maticity of the ring is restored by loss of a proton from the cyclohexadienyl cation... [Pg.477]

Complexation of bromine with iron(III) bromide makes bromine more elec trophilic and it attacks benzene to give a cyclohexadienyl intermediate as shown m step 1 of the mechanism (Figure 12 6) In step 2 as m nitration and sulfonation loss of a proton from the cyclohexadienyl cation is rapid and gives the product of electrophilic aromatic substitution... [Pg.480]

Two of the n electrons of benzene are used to form a bond to bromine and give a cyclohexadienyl cation intermediate... [Pg.481]

Step 2 Loss of a proton from the cyclohexadienyl cation yields bromobenzene... [Pg.481]

Figure 12 7 illustrates attack on the benzene ring by tert butyl cation (step 1) and subsequent formation of tert butylbenzene by loss of a proton from the cyclohexadienyl cation intermediate (step 2)... [Pg.482]

FIGURE 12 7 The mechanism of Friedel-Crafts alkylation The molecular model depicts the cyclohexadienyl cation intermediate formed in step 1... [Pg.482]

Why IS there such a marked difference between methyl and trifluoromethyl substituents m their influence on electrophilic aromatic substitution s Methyl is activating and ortho para directing trifluoromethyl is deactivating and meta directing The first point to remember is that the regioselectivity of substitution is set once the cyclohexadienyl cation intermediate is formed If we can explain why... [Pg.489]

One way to assess the relative stabilities of these various intermediates is to exam me electron delocalization m them using a resonance description The cyclohexadienyl cations leading to o and p mtrotoluene have tertiary carbocation character Each has a resonance form m which the positive charge resides on the carbon that bears the methyl group... [Pg.489]

When we examine the cyclohexadienyl cation intermediates involved m the nitra tion of (trifluoromethyl)benzene we And that those leading to ortho and para substitu tion are strongly destabilized... [Pg.492]

Sections How substituents control rate and regioselectivity m electrophilic aro 12 10-12 14 matic substitution results from their effect on carbocation stability An electron releasing substituent stabilizes the cyclohexadienyl cation inter mediates corresponding to ortho and para attack more than meta... [Pg.509]

Wnte a structural formula for the most stable cyclohexadienyl cation intermediate formed in each of the following reactions Is this intermediate more or less stable than the one formed by electrophilic attack on benzene" ... [Pg.513]

Cyclohexadienyl cation intermediate nitro group IS destabilizing... [Pg.980]

A nitro group is a strongly activating substituent in nucleophilic aromatic substitution where it stabilizes the key cyclohexadienyl anion intermediate... [Pg.980]

Cyclohexadienyl anion intermediate nitro group IS stabilizing... [Pg.980]

Here it is the combined electron attrachng effects of the six fluorine substituents that stabi hze the cyclohexadienyl anion intermediate and permit the reaction to proceed so readily... [Pg.980]

The rate determining intermediate is a cyclohexadienyl anion and is sta bilized by electron withdrawing substituents... [Pg.987]

Arenium ion (Section 12 2) The carbocation intermediate formed by attack of an electrophile on an aromatic substrate in electrophilic aromatic substitution See cyclohexadienyl cation... [Pg.1276]

Cycloalkene (Section 5 1) A cyclic hydrocarbon characterized by a double bond between two of the nng carbons Cycloalkyne (Section 9 4) A cyclic hydrocarbon characterized by a tnple bond between two of the nng carbons Cyclohexadienyl anion (Section 23 6) The key intermediate in nucleophilic aromatic substitution by the addition-elimination mechanism It is represented by the general structure shown where Y is the nucleophile and X is the leaving group... [Pg.1280]

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