A crotyl group is an
organic
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
with the formula .
Systematically, it is called a but-2-en-1-yl group and exhibits
geometric isomerism
Geometry (; ) is a branch of mathematics concerned with properties of space such as the distance, shape, size, and relative position of figures. Geometry is, along with arithmetic, one of the oldest branches of mathematics. A mathematician w ...
, being either ''cis'' (''Z'') or ''trans'' (''E''). There are many simple compounds in which the crotyl group forms base carbon chain:
crotyl alcohol
Crotyl alcohol, or crotonyl alcohol, is an unsaturated alcohol. It is a colourless liquid that is moderately soluble in water and miscible with most organic solvents. Two isomers of this alcohol exist, cis and trans.
It can be synthesized by th ...
,
crotonaldehyde
Crotonaldehyde is a chemical compound with the formula CH3CH=CHCHO. The compound is usually sold as a mixture of the ''E''- and ''Z''-isomers, which differ with respect to the relative position of the methyl and formyl groups. The ''E''-isomer i ...
,
crotonic acid
Crotonic acid ((2''E'')-but-2-enoic acid) is a short-chain unsaturated carboxylic acid described by the formula CH3CH=CHCO2H. The name crotonic acid was given because it was erroneously thought to be a saponification product of croton oil. It cr ...
, and
crotyl acrylate are examples.
Synthesis of
(crotyl anions) can be synthesised from
2-butene (either isomer): this reaction must be performed in the presence of
organometallic reagents, as a
base, usually
alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...
lithium
Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...
, or any
alkylate
An alkylation unit (alky) is one of the conversion processes used in petroleum refineries. It is used to convert isobutane and low-molecular-weight alkenes (primarily a mixture of propene and butene) into alkylate, a high octane gasoline componen ...
s of
''s''-block metals, in a solvent, typically
THF
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
, and at low temperatures, generally below -20 °C. The negative charge is delocalised over three of the carbon atoms of the group and there is resonance between the two possible delocalised forms (one for each terminal carbon).
Crotylation reactions
Crotylation readily occurs with
alkoxy
In chemistry, the alkoxy group is an alkyl group which is Single bond, singularly bonded to oxygen; thus . Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the ...
boronates to form .
are useful reagents in the formation of crotyl alcohols. They react with the acidic protons of
aldehydes
In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
to form alcohols. The mechanism involves a six-membered ring involving the carbonyl oxygen and boron in a chair-like structure. Such reactions are highly
diastereoselective
In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...
.
References
{{Functional groups
Alkenyl groups