Food chemistry
Comprising 75% of the biological world and 80% of all food intake for human consumption, the most common known human carbohydrate is Sucrose. The simplest version of a carbohydrate is a monosaccharide which contains carbon, hydrogen, and oxygen in a 1:2:1 ratio under a general formula of CHO where n is a minimum of 3. Glucose is an example of a monosaccharide as is fructose. Combine them in the picture shown to the right and you have sucrose, one of the more common sugar products around.
Theoretical astronomy
Infrared astronomy, for example, has revealed that the interstellar medium contains a suite of complex gas-phase carbon compounds called aromatic hydrocarbons, often abbreviated (PAHs or PACs). These molecules composed primarily of fused rings of carbon (either neutral or in an ionized state) are said to be the most common class of carbon compound in the galaxy. They are also the most common class of carbon molecule in meteorites and in cometary and asteroidal dust (cosmic dust). These compounds, as well as the amino acids, nucleobases, and many other compounds in meteorites, carry deuterium (H) and isotopes of carbon, nitrogen, and oxygen that are very rare on earth, attesting to their extraterrestrial origin. The PAHs are thought to form in hot circumstellar environments (around dying carbon rich red giant stars).