Organic chemistry is the chemistry of carbon and its huge number of compounds [1] . Carbon atoms can form extremely long chains and rings in various configurations, and bond with almost all other elements, building the base of life's super-complex molecules. Quantum mechanical models of the carbon atom’s cloud of electrons explain the bonding [2] . One of the most fundamental biochemical reactions is photosynthesis, the process by which plants turn inorganic carbon dioxide and water into organic compounds with the energy of light [3] .
More on detecting molecular structures
Tens of millions of carbon compounds (almost all of them organic) are known to exist, while the number of inorganic carbon-free compounds is less than a million. In the complex biochemical molecules, carbon bonds mainly with hydrogen and oxygen, but also with the nonmetals nitrogen, sulphur, and phosphorous, with halogens (like chlorine and iodine), and even with some metals.
The carbon atom’s cloud of electrons consists of 6 electrons in 4 orbitals configured in the ground state as follows: 2 electrons at the first (lowest) energy level in an s orbital, 2 electrons at the second energy level in an s orbital, and 2 electrons at the second energy level in two separate p orbitals of different spatial orientation and slightly higher energy than the s orbital (the s orbitals are spherical, while the p orbitals consist of two opposite balloon-like lobes tied together at the atom’s nucleus). In a chemical bond the outer s-electrons transit to a higher (excited) energy sub-level and then into hybrid sp orbitals (consisting of a small and a large lobe tied together at the nucleus). The hybridization allows for four different configurations, resulting in four different C-C bonds (single, double, triple, cyclic, see Sheet).
Photosynthesis produces energy-rich hydrocarbons, in particular sugars, that are essential for metabolism and respiration of almost all life. The total amount of the Sun’s energy captured by photosynthesis is several times greater than the world electricity consumption (but only less than 1% of the Sun’s irradiation). The process is the base for an annual biomass production of about 100 billion tons and the constant replenishment of the atmosphere with oxygen. All plants, algae, and marine cyanobacteria (previously thought to be blue-green algae) take part in oxygenic photosynthesis, using water as feedstock for hydrogen and atmospheric carbon dioxide as feedstock for carbon.