In general, all unsaturated alcohols belong to the class of alcohols, they have one or more corresponding functional hydroxogroups in their structure. They are distinguished only by the presence of multiple (double, triple) bonds in the molecule. Thus, unsaturated alcohols combine the properties of both unsaturated hydrocarbons and ordinary alcohols.
Building
As a rule, the hydroxo functional group should be at a saturated (that is, with only single bonds) carbon atom (the carbon atom located next to the functional group of the compound is called the alpha carbon). Such alcohols have all the standard properties of their limiting neighbors. The simplest unsaturated alcohol with a saturated alpha carbon is allyl alcohol or propendiol.
Enols
Alcohols with -OH group located near unsaturated carbon are called enols. Almost all of them are unstable and, upon formation, almost immediately rearrange into the corresponding ketones. A small part, however, remains in its original form, but it is quite small. In suchIn this case, they speak of keto-enol tautomerism: the substance simultaneously contains two so-called tautomers: in one, the hydrogen atom is located near oxygen, and this is enol, and in the other, hydrogen has moved to carbon, and this is already a ketone (carbonyl compound).
In most substances of this structure, the content of enols is a fraction of a percent. However, there are some compounds in which, due to certain substituents on the carbon atom directly bonded to the oxygen of the hydroxo group, relative stability of the enol can be achieved. For example, in acetylacetone, the percentage of enol tautomers reaches 76.
First in the enol series is vinyl alcohol. In the keto-enol tautomerism, it corresponds to acetaldehyde.
Chemical properties
Since unsaturated alcohols contain, as it were, two functional groups at once, the set of their reactions is also a combination of the properties of two classes of compounds. By a multiple bond, they, like all unsaturated hydrocarbons, react with the addition of halogens, hydrogen, hydrogen halides and other substances that form electrophilic particles. They can also form epoxides (when oxidized with atmospheric oxygen on a silver catalyst). Also, along the double group, unsaturated alcohols can attach additional hydroxyl groups to turn into di-, trihydric alcohols. The hydroxyl group itself enters into its typical reactions: oxidation (to the corresponding carbonyl compound, and then to the carboxylicacids), substitution by halogen, formation of ethers and esters.
Being in nature
Unsaturated alcohols are found in many parts of the living world. Most often they are there in the form of esters - compounds consisting of parts of alcohol and carboxylic acid. For example, cinnamon alcohol is found (in the form of esters of acetate and cinnamate) in hyacinth, cassia and other odorous oils, as well as in the composition of the resin in trees of the genus styrax and in Peruvian balsam - the resin of trees from the genus myroxylon. It is widely used in the perfume industry as a variety of fragrances and fragrances.
Retinol acetate - the well-known vitamin A. 3-hexenol-1 - cyclic unsaturated alcohol - in the composition of essential oils of green parts of plants gives the latter a characteristic smell.
Also, for example, the well-known cholesterol is an alcohol with a very complex formula, including multiple bonds (that's why in some countries they prefer to call the same substance cholesterol - according to the functional group). Accordingly, many substances related to cholesterol, in particular, some fatty alcohols, have a similar structure.
