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This question was answered well enough 5-7 years ago, but there is something still lacking. The resonance diagrams drawn in brackets suggest that resonance is responsible for increasing the acidity of phenol; I find the wording misleading. Better would be that the resonance of the phenyl ring is responsible for the stabilization of phenolate anion. IMHO, ...

7

Wouldn't it be the case that the molecule is actually in some hybrid state of trigonal planar and trigonal pyramidal? "Hybrid state" refers to the distribution of electrons, not nuclei. Different resonance structures can have different electron distributions, but they can't have nuclei in different places, which means that they can't have ...

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The other answer has given the major conformer of the protonated form of the o-hydroxybenzoic acid, but I believe there is a part of your question that still remains to be answered. You asked why the hydrogen bond makes the hydrogen bond more acidic than the para isomer, when the hydrogen bond is already present in the protonated form of the ortho-isomer. ...

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It is correct that the $\ce{N}$ with the double bond has a localized lone pair, because of its $sp^2$ hybridization, due to which the lone pairs are in the same plane as ring, and hence not conjugated. However, the other $\ce{N}$ is clearly in conjugation, hence, if you draw the $5$ possible resonance structures, you would notice that each bond in the ring ...

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after the shift, the positive charge occurs on phenyl which should be unstable. Are you sure about that? Firstly, the positive charge isn't 'on' the phenyl, it's on the Carbon to which the phenyl ring is attached and hence it enables resonance. Out of many of the factors we look for the stability of a carbocation (which include the ones you mentioned like ...

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Hammett $\sigma_m$ and $\sigma_p$ constants are based upon the acid dissociation of benzoic acid and m- and p-substituted benzoic acids $(\ce{X-C6H4-CO2H})$ in water at $\pu{25 ^\circ C}$. They are correlated with $K_\mathrm{a}$ values of these benzoic acids as shown in few examples in the following table:  \begin{array}{c|cccc} \hline \text{Substituent }(...

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If you check out the $\mathrm{p}K_\mathrm{a}$ values of paracetamol (acetaminophen) , it is 9.38 while $\mathrm pK_\mathrm a$ of para-methoxybenzene is 10.1. So, $\ce{-OR}$ should exert a greater mesomeric effect as compared to $\ce{-NHCOR}$ making the wikipedia wrong. References: https://pubchem.ncbi.nlm.nih.gov/compound/Acetaminophen https://pubchem.ncbi....

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Some of the conformers of salicylic acid are given below, all of which are planar in configuration.$\mathrm{^{[1]}}$ Although the compound can adopt several conformations the first conformer(in the first image, the structure on the left) is of the lowest energy and has a strong intramolecular hydrogen bond. The second conformer(first image, right structure) ...

3

We know that effect of neither hyperconjugation nor resonance is observed if the groups are attached in meta position. Hence, stability of structures I and IV will be decided on the basis of inductive effect only. Alkyl groups exert +I effect, and ethyl group exerts greater +I than methyl, hence stabilizing the electron deficient benzylic carbocation more. ...

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It would be interesting to know the sources cited in your question (both the book, as well as the primary literature) as reference because one complementary approach to the (assumed) spectroscopic determination is the analysis of the crystalline state. While there are multiple records about pure benzene, it seems there is no public model of the crystalline ...

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