1.1.1-Propellane
Encyclopedia
[1.1.1]Propellane is an organic compound
, the simplest member of the propellane
family. It is a hydrocarbon
with formula C5H6 or C2(=CH2)3. The molecular structure consists of three rings of three carbon
atoms each, sharing one C-C bond.
[1.1.1]Propellane is a highly strained molecule. The bonds of the two central carbon atoms have an inverted tetrahedral geometry, and the length of the central bond
is 160 pm. The strength of that bond
is disputed; estimates vary from 59–65 kcal/mol to no strength at all. The energy of the biradical state (without the central bond and unfilled central carbons) is calculated to be 80 kcal/mol higher. The compound is highly unstable, and at 114 °C it will spontaneously isomerize to 3-methylenecylobutene with a half-life of 5 minutes. Its strain energy
is estimated to be 102 kcal
/mol
(427 kJ/mol).
The type of bonding in this molecule has been explained in terms of charge-shift bonding
Sythesis begins with conversion of the 1,3-di-carboxylic acid
of bicyclo[1.1.1]pentane 1 in a Hunsdiecker reaction
to the corresponding dibromide
2 followed by a coupling reaction
with n-butyllithium
. The final product 3 was isolated by column chromatography
at -30°C (!)
However, a much simplified synthesis was published by . It starts with dibromocarbene
addition to the alkene
bond of 3-chloro-2-(chloromethyl)propene 6 followed by deprotonation
by methyllithium and nucleophilic displacements in 7 not isolated but kept in solution at −196 °C.
to yield a methylenecyclobutane ester
(4 above).
reaction where the central C-C bond is split and connected to adjacent monomer
units, resulting the so-called staffane
s.
A radical polymerization
initiated by methyl formate
and benzoyl peroxide
results in a distribution of oligomer
s. An anionic addition polymerization
with n-butyllithium
results in a fully polymerized product. X-ray diffraction of the polymer shows that the connecting C-C bonds have bond length
s of only 148 pm
The compound 1,3-dehydroadamantane
, which can be viewed as a bridged [1.3.3]Propellane, also polymerizes in a similar way.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
, the simplest member of the propellane
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...
family. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
with formula C5H6 or C2(=CH2)3. The molecular structure consists of three rings of three carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms each, sharing one C-C bond.
[1.1.1]Propellane is a highly strained molecule. The bonds of the two central carbon atoms have an inverted tetrahedral geometry, and the length of the central bond
Bond length
- Explanation :Bond length is related to bond order, when more electrons participate in bond formation the bond will get shorter. Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond will be shorter...
is 160 pm. The strength of that bond
Bond strength
In chemistry, bond strength is measured between two atoms joined in a chemical bond. It is the degree to which each atom linked to another atom contributes to the valency of this other atom...
is disputed; estimates vary from 59–65 kcal/mol to no strength at all. The energy of the biradical state (without the central bond and unfilled central carbons) is calculated to be 80 kcal/mol higher. The compound is highly unstable, and at 114 °C it will spontaneously isomerize to 3-methylenecylobutene with a half-life of 5 minutes. Its strain energy
Strain energy
In a molecule, strain energy is released when the constituent atoms are allowed to rearrange themselves in a chemical reaction or a change of chemical conformation in a way that:* angle strain,* torsional strain,* ring strain and/or steric strain,...
is estimated to be 102 kcal
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
/mol
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
(427 kJ/mol).
The type of bonding in this molecule has been explained in terms of charge-shift bonding
Synthesis
[1.1.1]Propellane was first synthesized by K. Wiberg and F. Walker in 1982,. according to the following schema:Sythesis begins with conversion of the 1,3-di-carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
of bicyclo[1.1.1]pentane 1 in a Hunsdiecker reaction
Hunsdiecker reaction
The Hunsdiecker reaction is the organic reaction of silver salts of carboxylic acids with halogens to give organic halides. It is an example of a halogenation reaction...
to the corresponding dibromide
Bromide
A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...
2 followed by a coupling reaction
Coupling reaction
A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...
with n-butyllithium
N-Butyllithium
n-Butyllithium is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene...
. The final product 3 was isolated by column chromatography
Column chromatography
Column chromatography in chemistry is a method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms.The main advantage of column chromatography is the relatively low cost and disposability...
at -30°C (!)
However, a much simplified synthesis was published by . It starts with dibromocarbene
Dichlorocarbene
Dichlorocarbene is a carbene commonly encountered in organic chemistry. This reactive intermediate with chemical formula CCl2 is easily available by reaction of chloroform and a base such as potassium t-butoxide or sodium hydroxide dissolved in water...
addition to the alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
bond of 3-chloro-2-(chloromethyl)propene 6 followed by deprotonation
Deprotonation
Deprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
by methyllithium and nucleophilic displacements in 7 not isolated but kept in solution at −196 °C.
Acetic acid addition
[1.1.1]Propellane spontaneously reacts with acetic acidAcetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
to yield a methylenecyclobutane ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
(4 above).
Polymerization
[1.1.1]propellane undergoes a polymerizationPolymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
reaction where the central C-C bond is split and connected to adjacent monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
units, resulting the so-called staffane
Staffane
A staffane or [n]staffane is an organic compound, a polycyclic hydrocarbon with molecular structure H-[-C≡3≡C-]n-H, for some integer n ≥ 1. The chemical formula is therefore C5nH6n+2...
s.
A radical polymerization
Radical polymerization
Free radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms usually involving separate initiator molecules...
initiated by methyl formate
Methyl formate
Methyl formate, also called methyl methanoate, is the methyl ester of formic acid. The simplest example of an ester, it is a clear liquid with an ethereal odor, high vapor pressure, and low surface tension.-Production:...
and benzoyl peroxide
Benzoyl peroxide
Benzoyl peroxide is an organic compound in the peroxide family. It consists of two benzoyl groups bridged by a peroxide link. Its structural formula is [C6H5C]2O2. It is one of the most important organic peroxides in terms of applications and the scale of its production...
results in a distribution of oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
s. An anionic addition polymerization
Anionic addition polymerization
Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups. This polymerization is carried out through a carbanion active species. Like all addition polymerizations, it...
with n-butyllithium
N-Butyllithium
n-Butyllithium is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene...
results in a fully polymerized product. X-ray diffraction of the polymer shows that the connecting C-C bonds have bond length
Bond length
- Explanation :Bond length is related to bond order, when more electrons participate in bond formation the bond will get shorter. Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond will be shorter...
s of only 148 pm
The compound 1,3-dehydroadamantane
1,3-Dehydroadamantane
1,3-Dehydroadamantane, formally tetracyclo[3.3.1.13,7.01,3]decane, is an organic compound with formula C10H14, which can be obtained from adamantane by removal of two hydrogen atoms to create an internal bond...
, which can be viewed as a bridged [1.3.3]Propellane, also polymerizes in a similar way.