WordNet

arrange into a group or groups; "Can you group these shapes together?"
(chemistry) two or more atoms bound together as a single unit and forming part of a molecule (同)radical, chemical group
any number of entities (members) considered as a unit (同)grouping
a set that is closed, associative, has an identity element and every element has an inverse (同)mathematical group
form a group or group together (同)aggroup
quantifier; used with either mass or count nouns to indicate the whole number or amount of or every one of a class; "we sat up all night"; "ate all the food"; "all men are mortal"; "all parties are welcome"
completely given to or absorbed by; "became all attention"
become an ally or associate, as by a treaty or marriage; "He allied himself with the Communists"
an associate who provides cooperation or assistance; "hes a good ally in fight" (同)friend
a friendly nation
the activity of putting things together in groups
a system for classifying things into groups (同)pigeonholing
the univalent unsaturated organic radical C3H5; derived from propylene (同)allyl_group, allyl radical

PrepTutorEJDIC

(…の)『群れ』,集まり,小集団《+of+名》 / (主義・系統・種類などを同じくする人・物の)『派』,『団体』 / (ポミュラーソング歌手の)グループ / (動・植物分類上の)群;(化学の)基,原子団;(地質学上の)界;(数学の)群;(言語学上の)語派 / …‘を'一群に集める,一団にする《+『名』+『together』》 / (系統的に)…‘を'分類する,調和よく配合する《+『名』+『together』》 / 集まる,群(集団)をなす
《単数形,または数えられない名詞につけて》(ある一つのものについて,その)『全体の』,全…,…じゅう,…全体 / 《複数形につけて》(個々を一つにまとめて)『全部の』,すべての / 《複数形,または数えられない名詞につけて》(ある全体の中の)いずれの,およそどの,あらゆる / 《数えられない名詞につけて》できる限りの,最大の / 《単数扱い》(物事について)『全部』,全体,すべて / 《複数扱い》『全員』,みんな / いっさいの所有物,いっさいがっさい / 『すっかり』,『全く』,もっぱら / 《all the+比較級の形で》かえって,いっそう / どちらも,双方とも
(…と)…'を'『同盟』(連合)『させる』《+『名』+『with』(『to』)+『名』》 / 同盟国 / 味方
グループに分けること;分類法 / (集まった物の)配置,配合

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/04/20 21:49:20」(JST)

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Structure of the allyl group.

resonance structure of the allyl anion

An allyl group is a substituent with the structural formula H₂C=CH-CH₂R, where R is the rest of the molecule. It consists of a methylene bridge (-CH₂-) attached to a vinyl group (-CH=CH₂). The name is derived from the Latin word for garlic, Allium sativum. In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil and named it "Schwefelallyl".^[1]^[2] The term allyl applies to many compounds related to H₂C=CH-CH₂, some of which are of practical or everyday importance.^{[clarification needed]}

Nomenclature and bonding

Allyl is a widely used term in organic chemistry.^[3] The unpaired electron is delocalized. Allylic radicals, anions, and cations are often discussed as intermediates in reactions. All feature three contiguous sp²-hybridized carbon centers.

MO diagram for pi-orbitals on allyl. The middle MO labeled Ψ₂ is singly occupied in the allyl radical. In the allyl cation Ψ₂ is unoccupied and in the allyl anion it is doubly occupied. Hydrogen atoms are omitted from this picture.

Allylic sites

A site on the saturated carbon atom is called the "allylic position" or "allylic site." A group attached at this site is sometimes described as "allylic." Thus, CH₂=CHCH₂OH "has an allylic hydroxyl group." Allylic C-H bonds are about 15% weaker than the C-H bonds in ordinary sp³ carbon centers and are thus more reactive. This heightened reactivity has many practical consequences. The industrial production of acrylonitrile by ammoxidation of propene exploits the easy oxidation of the allylic C-H centers.

2CH₃-CH=CH₂ + 2NH₃ + 3O₂ → 2CH₂=CH-C≡N + 6H₂O

Unsaturated fats spoil by rancidification involving attack at allylic C-H centers.

The free radical pathway for the first phase of the oxidative rancidification of fats.

Benzylic and allylic are related in terms of structure, bond strength, and reactivity. Other reactions that tend to occur with allylic compounds are allylic oxidations, ene reactions, and the Tsuji–Trost reaction. Benzylic groups are related to allyl groups; both show enhanced reactivity.

Pentadienyl

A CH₂ group connected to two vinyl groups is said to be doubly allylic. The bond dissociation energy of C-H bonds on a doubly allylic centre is about 10% less than the bond dissociation energy of a C-H bond that is allylic. The weakened C-H bonds reflect the high stability of the resulting "pentadienyl" radicals. Compounds containing the C=C-CH₂-C=C linkages, e.g. linoleic acid derivatives, are prone to autoxidation, which can lead to polymerization or form semisolids. This reactivity pattern is fundamental to the film-forming behavior of the "drying oils," which are components of oil paints and varnishes.

Homoallylic

The term homoallylic refers to the position on a carbon skeleton next to an allylic position. In but-3-enyl chloride CH₂=CHCH₂CH₂Cl, the chloride occupies a homoallylic position.

The allylic, homoallylic and doubly allylic sites are highlighted in red, respectively.

Allylation

Allylation is the process of adding an allyl group to a substrate. Typically allylation refers to the addition of an allyl anion equivalent to an organic electrophile:^[4]^[5] A typical allylation of an aldehyde (RCHO) is represented by the following two-step process that begins with allylation followed by hydrolysis of the intermediate:

RCHO + CH₂=CHCH₂M → CH₂=CHCH₂RCH(OM)

CH₂=CHCH₂RCH(OM) + H₂O → CH₂=CHCH₂RCH(OH) + MOH

A popular reagent for asymmetric allylation is the "Brown reagent", allyldiisopinocampheylborane.^[6]

Allyl derivatives

Many substituents can be attached to the allyl group to give stable compounds.

Organic compounds

Allyl alcohol, the parent of allylic alcohols, has the structure H₂C=CH-CH₂OH. Another example of a simple allyl compound is allyl chloride. Substituted versions of the parent allyl group, such as the trans-but-2-en-1-yl or crotyl group (CH₃CH=CH-CH₂-), may also be referred to as allylic groups. Many allylic compounds are lachrymatory.

Biochemistry

Dimethylallyl pyrophosphate is an allylic compound that is central in the biosynthesis of terpenes, a large family of naturally occurring organic compounds. Isopentenyl pyrophosphate, is a homoallylic isomer of the dimethylallyl compound. It also is the precursor to many natural products, including natural rubber.

Metal allyl complexes

The allyl ligand is commonly encountered in organometallic chemistry. Most commonly, allyl ligands bind to metals via all three carbon centers, the so-called η³-binding mode. Examples beyond those discussed below include Ir(η³-allyl)₃ and (η³-allyl)Mn(CO)₄. Some complexes with η¹-allyl ligands are also known, e.g., CpFe(CO)₂(η¹-allyl) where only the methylene group is attached to the Fe centre. Such compounds often convert to the η³-allyl derivatives by dissociation of a ligand:

CpFe(CO)₂(η¹-allyl) → CpFe(CO)(η³-allyl) + CO

Allyl complexes are usually generated by oxidative addition of allylic halides to low-valent metal complexes. This route affords pi-allyl nickel compounds, such as (allyl)₂Ni₂Cl₂:^[7]

2 Ni(CO)₄ + 2 ClCH₂CH=CH₂ → Ni₂(μ-Cl)₂(η³-C₃H₅)₂ + 8 CO

In terms of applications, a popular allyl complex is allyl palladium chloride. Allyl ligands are susceptible to nucleophilic addition, which can be useful in organic synthesis.^[8]

Structure of allylpalladium chloride dimer.

References

^ Theodor Wertheim (1844). "Untersuchung des Knoblauchöls". Annalen der Chemie und Pharmacie 51 (3): 289. doi:10.1002/jlac.18440510302.
^ Eric Block (2010). Garlic and Other Alliums: The Lore and the Science. Royal Society of Chemistry. ISBN 0-85404-190-7.
^ Jerry March, “Advanced Organic Chemistry” 4th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
^ http://www.chem.umn.edu/groups/harned/classes/8322/lectures/2AllylationReactions.pdf
^ S. E. Denmark, J. Fu "Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones" Chem. Rev., 2003, vol. 103, pp 2763–2794. doi:10.1021/cr020050h
^ Y. Yamamoto, N. Asao "Selective reactions using allylic metals" Chem. Rev., 1993, vol. 93, pp 2207–2293. doi:10.1021/cr00022a010
^ Martin F. Semmelhack and Paul M. Helquist (1988), "Reaction of Aryl Halides with π-Allylnickel Halides: Methallylbenzene", Org. Synth. ; Coll. Vol. 6: 722
^ Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN 189138953X

Appendix

A representative triglyceride found in linseed oil features groups with both singly and doubly allylic CH₂ sites (linoleic acid and alpha-linolenic acid) and singly allylic sites (oleic acid).

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