What is cyclopropane?

The cyclopropane  is a cyclic molecule having the molecular formula C 3 H 6 , and consisting of three carbon atoms joined together to form a ring. In chemistry there is a family of saturated hydrocarbons that have a backbone made up of carbon atoms joined by single bonds in the form of a ring.

This family consists of a varied number of molecules (which differ by the length of their main carbon chain), and are known to have higher melting and boiling points than those of high chains, as well as a greater reactivity than these.

Cyclopropane was discovered in 1881 by an Austrian chemist named August Freund, who was determined to know what was the toxic element in ethylene and who came to think that it was the same cyclopropane.

Even so, it was not until the 1930s that it began to be produced on an industrial level, when they discovered its uses as anesthesia, because before that time they did not find it commercially attractive.

Chemical structure

Cyclopropane, with the molecular formula C 3 H 6 , consists of three small carbon atoms that join in such a configuration that a ring is formed, leaving a molecular symmetry of D 3h at each carbon in the chain.

The structure of this molecule requires that the bond angles that are formed be around 60º, much less than the 109.5º observed between sp 3 hybrid atoms , which is a more thermodynamically stable angle.

This leads to the ring suffering from a more significant structural stress than other structures of this type, in addition to a natural torsional stress that it possesses due to the eclipsed conformation of its hydrogen atoms.

For this same reason, the bonds that form between the carbon atoms in this molecule are considerably weaker than in common alkanes.

In a peculiar way and unlike other bonds where the proximity between two molecules symbolizes greater bond energy, the bonds between the carbons of this molecule have a particularity of having a shorter length than the other alkanes (due to their geometry), and at the same time they are weaker than the unions between them.

Furthermore, cyclopropane possesses the stability by cyclic delocalization of the six electrons in the carbon-carbon bonds, being slightly more unstable than cyclobutane and considerably more than cyclohexane.

Properties of cyclopropane

Boiling point

Compared to the other more common cycloalkanes, cyclopropane has the lowest boiling point among these types of molecule, voltatilizing at minus 33 degrees (no other cycloalkanes volatilize at temperatures below zero).

On the other hand, compared to linear propane, cyclopropane has a higher boiling point: it volatilizes at minus 42 ° C, slightly lower than that of its cycloalkane cousin.

Melting point

The melting point of cyclopropane is lower than that of other cycloalkanes, melting at a temperature of 128 ºC lower than zero. Even so, it is not the only cycloalkane that melts at a temperature below zero, and this phenomenon can also be observed in cyclobutane, cyclopentane and cycloheptane.

So, in the case of linear propane, it melts at a temperature lower than 187 ° C below zero.


Cyclopropane has the highest density among cycloalkanes, being more than two times higher than the densest common cycloalkane (1.879 g / l for cyclopropane, surpassing cyclodecane with 0.871).

A higher density is also observed in cyclopropane than in linear propane. The difference in boiling and melting points between linear alkanes and cycloalkanes is due to higher London forces, which are increased by the ring shape that allows a greater contact area between internal atoms.


The reactivity of the cyclopropane molecule is directly affected by the weakness of its bonds, increasing considerably compared to other cycloalkanes due to the stress exerted on these bonds.

Thanks to this, cyclopropane can be separated more easily, and can behave as an alkene in certain reactions. In fact, the extreme reactivity of cyclopropane-oxygen mixtures can become an explosion hazard.

Uses / applications

The commercial use of cyclopropane par excellence is as an anesthetic agent, this property being studied for the first time in 1929.

Cyclopropane is a powerful, fast-acting anesthetic agent that does not irritate the airways or have a bad odor. It was used for several decades together with oxygen to put patients to sleep during surgery, but unwanted side effects began to be observed, represented as “cyclopropane shock.”

Along with the factors of cost and high flammability, it went through a process of discarding and replacing it with other safer anesthetic agents.

Although it continued to be part of the compounds used in the induction of anesthesia, today it is not part of the agents used in medical applications.


– Cyclopropane is a highly flammable gas, which produces toxic gases when it comes into contact with a flame. In addition, it can react with oxidizing agents such as perchlorates, peroxides, permanganates, nitrates and halogens, causing fires and / or explosions.

– High levels of cyclopropane can cause headaches, dizziness, nausea, loss of coordination, feeling faint and / or lightheaded.

– It can also cause irregularities in the heart rhythm or arrhythmia, breathing difficulties, coma and even death.

– The liquefied cyclopropane can cause frostbite on the skin due to its temperature considerably below zero.

– Because it is a gas under ambient conditions, this compound can easily enter the b

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