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Cyclobutane

physical science Maturity 11-13 Next article →

Cyclobutane is a specific type of organic compound known as a cycloalkane. It is defined by the chemical formula (CH2)4. In its natural state, cyclobutane is a colorless gas. It can also be found commercially as a liquefied gas. While the simple cyclobutane molecule has no major commercial or biological use, its derivatives are very important. These derivatives are molecules that contain the cyclobutane structure. They play vital roles in the fields of biology and biotechnology.

CyclobutaneConf2
CyclobutaneConf2

The structure of this molecule is defined by intense internal tension. The bond angles between the four carbon atoms are significantly strained. This strain means the bonds have lower energies than related hydrocarbons. For example, butane and cyclohexane are unstrained and more stable. Because of this high energy, cyclobutane becomes unstable above 500 °C. The four carbon atoms do not sit on a flat plane. Instead, the ring adopts a folded or "puckered" conformation. This shape is often called a "butterfly" conformation.

CyclobutaneConf2
CyclobutaneConf2

This puckered shape is a clever way for the molecule to exist. In this conformation, the C-C-C angle is less than 90°. One specific carbon atom sits at a 25° angle from the plane of the other three. By folding this way, the molecule reduces some of its eclipsing interactions. These interactions are the stresses caused by atoms being too close together. The molecule can also switch between different equivalent puckered conformations. This movement allows the ring to manage its inherent structural strain.

Nature uses these strained rings in surprising biological ways. One example is pentacycloanammoxic acid, which is a type of ladderane. A ladderane is made of five fused cyclobutane units. This compound has an estimated strain three times higher than a single cyclobutane ring. It is found in bacteria that perform the anammox process. These bacteria use the molecule to form a very dense membrane. This tight membrane protects the organism from toxic substances like hydrazine and hydroxylamine. These chemicals are part of the process that turns nitrite ions and ammonia into nitrogen and water.

Pentacycloanammoxic acid
Pentacycloanammoxic acid

Light can also cause cyclobutane structures to form in living cells. This happens through a photochemical reaction called a photodimer. This occurs when the C=C double bonds of pyrimidines couple together. The most common version is the thymine dimer, or T-T dimer.

Thymine photodimer
Thymine photodimer

Most organisms have ways to fix this damage. They use nucleotide excision repair enzymes to repair the DNA. Other organisms use a family of light-dependent enzymes called photolyases. These enzymes use light to help fix the chemical bonds.

When these repair systems fail, it can lead to serious health issues. Xeroderma pigmentosum is a genetic disease that affects this repair process. People with this condition cannot properly fix the damage caused by UV light. This failure can result in skin discoloration and the development of tumors. However, cyclobutane structures can also be used for good in medicine. A well-known anticancer drug called carboplatin is used to treat patients. This drug is derived from cyclobutane-1,1-dicarboxylic acid.

Thymine photodimer
Thymine photodimer

Scientists have known how to create these molecules for over a century. Cyclobutane was first synthesized in 1907. Two scientists, James Bruce and Richard Willstätter, achieved this discovery. They created it by hydrogenating cyclobutene in the presence of nickel. Today, chemists use many different methods to prepare cyclobutanes in laboratories. Some methods involve the dimerization of alkenes using UV light irradiation. In the Norrish-Yang reaction, irradiated carbonyls cyclize to form a cyclobutanol. Other methods include ketenes attacking electron-rich alkenes to create cyclobutanones. Finally, 1,4-dihalobutanes can be converted into cyclobutanes through dehalogenation with reducing metals.

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File:CyclobutaneConf2.png
CyclobutaneConf2.png
File:Pentacycloanammoxic acid.svg
Pentacycloanammoxic acid.svg
File:Thymine photodimer.svg
Thymine photodimer.svg
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