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The following question was given in NCERT Exemplar Problems (Class XII): enter image description here

According to Wikipedia:

In organic chemistry, the aromatic alcohols or aryl-alcohols are a class of chemical compounds containing a hydroxyl group (—OH) bonded directly to an aromatic hydrocarbon group, in contrast to the benzyl alcohol, where the hydroxyl group is bonded indirectly to an aromatic carbon atom.

But, I didn't understood the part: aromatic alcohols or aryl-alcohols (as aromatic alcohols are not always aryl alcohols).

Further, we know that aryl halides are compounds in which halogen group (-X) is directly attached to an aromatic ring. In the same way, aryl alcohols also mean that those compounds in which hydroxyl group (-OH) is directly attached to an aromatic ring.

Hence, according to my understanding, the answer should be (ii), but the answer given is (iii).

Where I am wrong? And, what is an aromatic alcohol?

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  • $\begingroup$ Sometimes phenols (OH group connected to the aromatic ring) are not considered to be alcohols, basically because they are much more acidic than aliphatic alcohols. When you use such a convention, aromatic alcohols are those in which you have an aromatic ring and a hydroxyl group connected to a sp3 carbon. If NCERT follow this convention, the right answer would be III. $\endgroup$ – Raul Luciano Jun 13 '18 at 18:45
  • $\begingroup$ @RaulLuciano seems to make the correct distinction based on current terminology. From IUPAC gold book alcohols are Compounds in which a hydroxy group, –OH, is attached to a saturated carbon atom $\ce{R3COH}$. Phenols are compounds having one or more hydroxy groups attached to a benzene or other arene ring. // So is "aromatic alcohol" outdated terminology? $\endgroup$ – MaxW Jun 13 '18 at 19:09
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    $\begingroup$ @MaxW aromatic alcohol is still used, but it means a compound which has both the alcohol group and an aromatic ring in its structure. $\endgroup$ – Raul Luciano Jun 13 '18 at 19:58
  • $\begingroup$ @RaulLuciano, My question is why Wikipedia has said "aromatic alcohols or aryl alcohols" as aryl alcohols are Ar-OH which is not congruent to your definition of aromatic alcohols ? $\endgroup$ – rv7 Jun 14 '18 at 4:04
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    $\begingroup$ @Rahul It should be pointed out that Wikipedia is not to be considered an authoritative source and has many incongruities and errors of fact. $\endgroup$ – Dr. J. Jun 14 '18 at 10:36
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'Aromatic alcohol' is not a term that appears anywhere in the IUPAC literature - while its meaning is evident, it doesn't make sense in the same way that 'aromatic heterocyclic' does so is probably best avoided. What is defined by IUPAC is the definition of a phenol, and the definition of an aryl group. The definitions below come from an old IUPAC glossary of 'class names' which, although old, is still referenced in the most recent organic nomenclature guidelines and the most recent IUPAC Gold Book.

phenols: Compounds having one or more hydroxy groups attached to a benzene or other arene ring

aryl groups: Groups derived from arenes by removal of a hydrogen atom from a ring carbon atom.

Glossary of Class Names of Organic Compounds and Reactive Intermediates Based on Structure. Pure App. Chem. 1995, 67, 1307

To actually answer your question, the answer is (II) - as Jerepierre alluded to, the NCERT books / guides are renowned for being less that accurate, and a quick search around chem.SE will reveal just how many errors there are! In this case, its hard to tell if the error is just due to typesetting (someone typed III instead of II), or it it lies with the ambiguity of the term 'aromatic alcohol' (is it referring to phenols, or is it referring to a compound which contains both an aryl ring and a hydroxyl group).

I think its fair to assume that the question is asking you to identify the phenols, in which case the answer is (II) is because A and D are the only structures in which the hydroxyl group is directly attached to a benzene or other arene ring, which is our working definition of a phenol / aromatic alcohol.

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    $\begingroup$ So, according to you, aromatic alcohol is not defined anywhere in the world of chemistry. Right? $\endgroup$ – rv7 Jun 16 '18 at 15:20
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    $\begingroup$ No. Just according to me its an ambiguous term and not one used by IUPAC (the people who define the Internationally accepted system of nomenclature). $\endgroup$ – NotEvans. Jun 16 '18 at 15:31
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Compound which contain an - OH group in a side chain attached to an aromatic ring is known as aromatic alcohol. So option number (iii) is correct

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