.1.1ropellane is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

, the simplest member of the

propellane In organic chemistry, propellane is any member of a class of polycyclic hydrocarbons, whose carbon skeleton consists of three rings of carbon atoms sharing a common carbon–carbon covalent bond. The concept was introduced in 1966 by D. Ginsbu ...

family. It is a

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

with formula or . The molecular structure consists of three rings of three

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

atoms each, sharing one C–C bond. .1.1ropellane is a highly strained molecule. The bonds of the two central carbon atoms have an

inverted tetrahedral geometry In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−) = 109.4712206...° ≈ 109.5° when all four substituents are ...

, and the length of the central bond is 160 pm. The strength of that bond is disputed; estimates vary from 59–65

kcal The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...

/ mol to no strength at all. The energy of the biradical state (with no central bond at all) is calculated to be 80 kcal/mol higher. At 114 °C it will spontaneously isomerize to 3-methylidenecyclobutene (5 below) with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of 5 minutes. Its

strain energy In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) force is called strain energy. For Linear elasticity, linearly elastic materials, strain energy is: : U = \frac 1 2 V \sigma \epsilon = \frac ...

is estimated to be 102 kcal/mol (427 kJ/mol). Surprisingly, .1.1ropellane is persistent at room temperature and is somewhat less susceptible to thermal decomposition than the less strained (90 kcal/mol) .2.2ropellane system, which has an estimated half-life of only about 1 h at 25 °C. This unusual stability is attributed to delocalisation of electron density from the bond between the central carbon atoms onto the bridging carbon atoms. The type of bonding in this molecule has been explained in terms of

charge-shift bond In theoretical chemistry, the charge-shift bond is a proposed new class of chemical bonds that sits alongside the three familiar families of covalent, ionic, and metallic bonds where electrons are shared or transferred respectively. The charge sh ...

ing.

Synthesis

.1.1ropellane was first reported by K. Wiberg and F. Walker in 1982. The synthesis commences with

cyclopropanation In organic chemistry, cyclopropanation refers to any chemical process which generates cyclopropane () rings. It is an important process in modern chemistry as many useful compounds bear this motif; for example pyrethroids and a number of quinolon ...

of 1,1-bis(chloromethyl)ethylene, according to the following scheme: : 111propellaneSynthesis

Synthesis begins with conversion of the 1,3-di-

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

of bicyclo .1.1entane 1 in a

Hunsdiecker reaction The Hunsdiecker reaction (also called the Borodin reaction or the Hunsdiecker–Borodin reaction) is a name reaction in organic chemistry whereby silver salts of carboxylic acids react with a halogen to produce an organic halide. It is an e ...

to the corresponding di

bromide A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...

2 followed by a

coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = ...

with ''n''-butyllithium. The final product 3 was isolated by

column chromatography Column chromatography in chemistry is a chromatography method used to isolate a single chemical compound from a mixture. Chromatography is able to separate substances based on differential adsorption of compounds to the adsorbent; compounds move th ...

at −30 °C. However, a much simplified synthesis was published by Szeimies. It starts with

dibromocarbene Dichlorocarbene is the reactive intermediate with chemical formula CCl2. Although this chemical species has not been isolated, it is a common intermediate in organic chemistry, being generated from chloroform. This bent diamagnetic molecule rapid ...

addition to the

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

bond of 3-chloro-2-(chloromethyl)propene 6 followed by

deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

methyllithium Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in so ...

and

nucleophilic displacement In chemistry, a nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). The ...

s in 7 not isolated but kept in solution at −196 °C.

Reactions

Acetic acid addition

.1.1ropellane spontaneously reacts with

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...

to yield a methylidenecyclobutane

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

(4 above).

Polymerization

.1.1ropellane undergoes a

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are ...

reaction where the central C–C bond is split and connected to adjacent

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

units, resulting in

staffane A staffane or taffane is an organic compound, a polycyclic hydrocarbon with molecular structure H- C≡(-CH2-)3≡C-sub>''n''-H, for some integer ''n'' ≥ 1. The chemical formula is therefore C5''n''H6''n''+2 Staffanes were first obtained in 1 ...

s. :

radical polymerization In polymer chemistry, free-radical polymerization (FRP) is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks ( repeat units). Free radicals can be formed by a number of different mechani ...

initiated by

methyl formate Methyl formate, also called methyl methanoate, is the methyl ester of formic acid. The simplest example of an ester, it is a colorless liquid with an ethereal odour, high vapor pressure, and low surface tension. It is a precursor to many other co ...

and

benzoyl peroxide Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...

results in a distribution of

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

s. An

anionic addition polymerization In polymer chemistry, anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but tradi ...

with ''n''-butyllithium results in a fully polymerized product.

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

of the polymer shows that the connecting C–C bonds have

bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...

s of only 148 pm. The compound 1,3-dehydroadamantane, which can be viewed as a bridged .3.3ropellane, also polymerizes in a similar way.

References

{{DEFAULTSORT:Propellane, 1.1.1 Bicycloalkanes Tricyclic compounds

Synthesis

Reactions

Acetic acid addition

Polymerization

See also

References