Today’s Image of the Day from NASA Earth Observatory shows the global distribution of a molecule called the hydroxyl (OH) radical. This highly reactive molecule acts like a detergent as it sweeps through the air, breaking down other gases such as methane. The molecule that can recycle itself

The map in the image is based on a model by atmospheric chemist Julie Nicely of NASA’s Goddard Space Flight Center, and shows the global production of OH on July 1, 2000.

“OH concentrations are pretty stable over time,” said Nicely. “When OH reacts with methane, it does not necessarily go away, especially in the presence of nitrogen oxides (NO and NO2). The breakdown products from the reaction with methane then react with NO or NO2 to reform OH again. So OH can recycle back into the atmosphere.”

A hydroxy or hydroxyl group is the entity with the formula OH. It contains oxygen bonded to hydrogen. In organic chemistry, alcohols and carboxylic acids contain hydroxy groups. Both the negatively charged anion OH−, called hydroxide, and the neutral radical •OH, known as the hydroxyl radical, consist of an unbounded hydroxyl group.
According to IUPAC rules, the term hydroxyl refers to the hydroxyl radical (•OH) only, while the functional group −OH is called hydroxy group.

Water, alcohols, carboxylic acids, and many other hydroxy-containing compounds can be deprotonated readily. This behavior is rationalized by the disparate electronegativities of oxygen and hydrogen. Hydroxy-containing compounds engage in hydrogen bonding, which causes them to stick together, leading to higher boiling and melting points than found for compounds that lack this functional group. Organic compounds, which are often poorly soluble in water, become water-soluble when they contain two or more hydroxy groups, as illustrated by sugars and amino acid.

By Chrissy Sexton, Staff Writer

Image Credit: NASA Earth Observatory


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