Methyl isobutyl ketone (4-methyl-2-pentanone, hexone, MIBK).
1,2-ethanediol 1-Cyclohexyl-1-butanol 1-Cyclohexyl-1-hydroxypentane 1-Cyclohexyl-1-pentanol 1-Cyclohexyl-1-propanol 1-Cyclohexyl ...
A: Those are electron withdrawing through inductive effects, which is one part of the overall effect. You also have to consider resonance effects, which can sometimes outweigh the inductive effect. This is the case for the -OH of phenol, -OCH3 of anisole, -NH2 for aniline, etc. These groups have a more electronegative atom (than C) attached to the benzene ring and therefore have an electron withdrawing inductive effect. However, these groups have a very strong electron donating resonance effect which outweighs the inductive effect, and therefore the overall effect for these substituents is that they are strong electron donating groups.
Cyclohexyl bromide; Molecular Formula: C 6 H 11 Br
A: A substituent on a benzene ring is regarded as activating when the substituted benzene is more reactive toward electrophilic aromatic substitution than benzene itself. Another way to look at it is that rate of electrophilic aromatic substitution for toluene, phenol, aniline, anisole, etc., is faster than the rate of electrophilic aromatic substitution for benzene. A deactivator is the opposite. The rate of electrophilic aromatic substitution for chlorobenzene, nitrobenzene, benzaldehyde, etc. is slower than the rate of electrophilic aromatic substitution for benzene.
The activator or deactivator designation therefore pertains to relative reactivity of the substituted benzene. Things that donate electrons make the benzene ring more electron rich and therefore more nucleophilic (faster reaction with electrophiles). Substituents that withdraw electrons make the benzene ring electron deficient, and therefore less nucleophilic because the electron are less available (slower rate of reaction with electrophiles).
The question of ortho-para versus meta directing pertains to how the substituent influences the relative stability of the intermediate carbocations from electrophilic addition. For electrophilc addition at the ortho or para positions, the positive charge of the carbocation resonances structures are spread out on the same carbons of the benzene ring (see Figures 16.12, 16.13, 16.14, and 16.15). The charge is on a different set of carbons for electrophilic addition to the meta position. The directing effect can be rationalized by analyzing the influence of the substituent on the carbocation resonance structures. We find that a carbocation resonance structure that arises from either ortho or para addition of the electrophile, places the positive charge on the carbon bearing the substituent. If the substituent is electron donating (either by inductive effects or resonance), the change can be stabilized by the substituent (see the boxed structures in Figure 16.12, 16.13 and 16.14). Thus, ortho or para addition is favored. If the substituent has an electron withdrawing resonance effect, the charge is destablized for this same carbocation resoanance structure from ortho or para addition (see the boxed structure in Figure 16.15). In this case, ortho or para addition is disfavored, leading to meta addition. While the carbocation for meta addition, is still detabilized by the elctron withdrawing group, it is less destabilzed than for ortho or para addition because none of the resonance structures place the charge next to the electron withdrawing group.
So the reason there are no meta directing activators is because the carbocation intermediate from ortho or para addition will always be more stable for an activating group.
The nature of the catalyst (Lewis acid) is central to all of this. The Lewis acids catalysts for electrophilic aromatic substitution are not necessarily interchangeable and there is a continuum of reactivities. FeX3 is strong enough to activate X2 for electrophilic substitution with a variety of substituted benzenes and does not have the drawbacks noted above. However, FeX3 is not a strong enough LA catalyst to generate a carbocation from an alkyl halide in most cases. So FeX3 is not a common FC alkylation catalyst.
The FC acylation suffers from many of the same drawbacks. Most oxacarbenium ions, although highly reactive, are not as fragile as alkyl carbocation. However, they react with amines and alcohols (anilines and phenols) to give amides and esters rather than the aromatic ring to give electrophilic substitution products. For F-C acylation, a stoichiometric amount of the Lewis acid catalyst is required since after electrophilic aromatic substitution the aryl ketone product will form a complex with the catalyst and prevent it from turning over.
So overall, we see that there is a narrow window of substituted benzenes for FC reactions: benzene itself, simple alkyl benzenes, halobenzenes, phenols and anisoles (or any ether of phenol). This needs to be taken into account in planning the order of reactions for a synthesis problem along with the directing effects.
2-methyl butyl acetate, 624-41-9 - The Good Scents …
A: A substituted benzene is considered deactivated if the rate of electrophilic substitution is slower than for benzene. Activated is just the opposite, the rate of electrophilic substitution is faster than for benzene. The change in rate is attributed to the influence of the substituent on the pi-electrons of the aromatic ring. In general, if the net effect of the substituent is that it is electron withdrawing, the ring is deactivated. An electron withdrawing pulls electron density away from the aromatic ring making it electron deficient and consequently less nucleophilic. Electron donating groups push electron density toward the aromatic ring making it more electron rich and more nucleophilic.
The two components for determining if a substituent activates or deactivates the aromatic ring are its inductive and resonance effect. This is summarized on Table Table 16.2 and Figure 16.10. There is related discussion on these issue below.
Problem 16.31 asks you to predict where FC alkylation will occur on the given substituted benzene. FC alkylation is not compatible for all substituted benzenes and these limitations are noted in Figure 16.8. FC alkylation works for benzene, alkyl benzenes, phenols, anisoles, and halobenzenes. If does not work for other deactivated benzenes and for anilines. There is related discussion on this issue below.
(a) bromobenzene is slightly deactivated and there are no incompatible functional groups. It will undergo FC alkylation at the ortho or para-positions.
(b) m-bromophenol has a modest deactivating group and a strong activating group so overall it is activated. There are no incompatible functional groups. The directing effect for the two groups reinforce so you would expect FC alkylation to occur at the 4- and 6-positions
(c) p-chloroaniline, although aniline is an activating group it is incompatible with the FC alkylation reaction and therefore gives no reaction.
(d) 2,4 dichloronitrobenzene, this compound has three deactivating groups on it so it is strongly deactivated. A single nitro group is enough to prevent FC alkylation- no reaction
(e) 2,4-dichlorophenol. The two chloro groups are each modestly deactivating groups but the phenol is strongly activating. Overall, this is still an activated aromatic. There are no incompatible functional groups. The directing effect of the two chlorine atoms reinforce each other but are oppose the directing effect of the phenol. The phenol wins because it is the more powerful activator. FC alkylation occurs at the 6- position.
(f) benzoic acid is deactivated so this does not react in an FC alkylation
(g) p-methylsulfonic acid, the methyl group is a modest activator, the sulfonic acid group is a strong deactivator. The next effect is that the aromatic ring is deactivated and does not undergo FC alkylation.
(h) 2,5-dibromotoluene, The two bromine substituents are modestly deactivating while the methyl group is modest activator. The net effect is that the ring is probably not much different than benzene itself, perhaps very modestly activated, perhaps very modestly deactivated. It certainly is not strongly deactivated and there are no incompatible function groups. The directing effect of the two bromine oppose each other. The directing effect of the methyl group reinforces with the 5-bromo but is opposed to the 2-bromo. The methyl group is the stronger activating group and will direct the FC-alkylation to the 4-position.
A: If two groups are meta to one another, then it is hard to but a third group in between the two existing meta-substituents to give a 1,2,3-trisubstituted benzene. In this case, the NH2 and Cl are para, so putting the third group on isn't a problem.
134 results found for keyword 1-cyclohexyl-2-methyl-propan-2-ol
methyl 2-cyclohexyl-2-hydroxyacetate | C9H16O3 - …
need to 1-Butanol,2-[[5-methyl-2-(1-methylethyl)cyclohexyl ..
product is 2-cyclopropyl-3,3-dimethyl-2-butanol
a detailed synthetic plan based on your chosen retrosynthesis for the synthesis of 2-cyclohexyl-2-butanol.
CAS 2-methyl-3-phenyl-2-butanol 2 ..
A: Yes, that bis-Grignard reagent is actually known. Although it was not used as you described, its reaction with methyl acetate would give 1-methylcyclohexanol.
Compound 4r (2E)-N-Cyclohexyl-2-methyl-3 ..
A: Addition of methylmagniesium bromide to any ester of benzoic acids (i.e., ethyl benzoate) is a perfectly good way to make 2-phenyl-2-propanol.
Synthesis of 3-Cyclohexyl-2-Methylquinazolin-4 ..
The structure you propose (probably 2,6-di-t-butylbenzyl alcohol or (2,6-di-t-butylphenyl)methanol) would have a more complicated aromatic pattern and it would intergate to three rather than two protons. The three adjacent proton would couple to one another to give two doublet and a doublet of doublets. The fact that the aromatic protons are one singlet indicates that there are no aromatic protons on adjacent carbons and they are related by symmetry. (your proposed structure has the correct symmetry element)
The only other structure that would be acceptable (i.e., consistent with the data) is exchanging the methyl and hydroxyl groups. Since the two t-butyl groups are equivalent in the 1H NMR, they must also be related by a symmetry plane.
(SEE Cyclohexyl Bromide) 10346: ..
A: Like Grignard reagents, Gilman reagents are strong bases, so having a free OH as part of the reagent would not work. The downside to the strategy you suggest is that BrCH2OH is not a stable compound (you wouldn't necessarily know that), so you couldn't even protect it as a TMS ether. There is an alternative protecing group that could be used, CH3OCH2OCH2Cl, which is known and would work. The CH3OCH2- can be removed with Lewis acids. I digresss and you shouldn't worry about this.
So the better strategy using the tools we have learned is to make the Grignard reagent from bromocyclohexane and react it with formaldehyde (H2C=O). See page 602.
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