Carminic acid is a red glucosidal hydroxyanthrapurin that occurs naturally in some scale insects, such as the cochineal and the Polish cochineal. The insects produce the acid as a deterrent to predators. Carminic acid is the colouring agent in carmine.

Chloral hydrate is a sedative and hypnotic drug as well as a chemical reagent and precursor. The name chloral hydrate indicates that it is formed from chloral (trichloroacetaldehyde) by the addition of one molecule of water. Its chemical formula is C₂H₃Cl₃O₂.

Chlorhexidine is a chemical antiseptic. It is effective on both Gram-positive and Gram-negative bacteria, although it is less effective with some Gram-negative bacteria.

Chlorodifluoromethane is a hydrochlorofluorocarbon (HCFC). It is commonly used as a propellant and in air conditioning applications. It is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.

Carvacrol, is a monoterpenoid phenol. It has a characteristic pungent, warm odour of oregano and a pizza-like taste.

tert-Butyl chloride is a colourless, liquid organic compound at room temperature. The compound is flammable and volatile, and its main use is as a starting molecule to carry out nucleophilic substitution reactions, to produce different substances, ranging from alcohols to alkoxide salts.

Chlorothiazide sodium (Diuril) is a diuretic used within the hospital setting or for personal use to manage excess fluid associated with congestive heart failure. It is also used as an antihypertensive.

Vitamin K is a group of structurally similar, fat soluble vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation but also involved in metabolic pathways in bone and other tissues.

Chloroquine is a 4-aminoquinoline drug used in the treatment or prevention of malaria.

Choline is a water-soluble essential nutrient. It is usually grouped within the B-complex vitamins. Choline generally refers to the various quaternary ammonium salts.

The organic compound citrulline is an α-amino acid. Although citrulline is not coded for by DNA directly, several proteins are known to contain citrulline as a result of a posttranslational modification.

Factor IX or Christmas factor is one of the serine proteases of the coagulation system; it belongs to peptidase family S1. Deficiency of this protein causes hemophilia B.

cis-3-Hexenal is one of the major volatile compounds in ripe tomatoes. It is produced in small amounts by most plants and it acts as an attractant to many predatory insects. It is also a pheromone in many insect species.

Cloxacillin is a semisynthetic antibiotic in the same class as penicillin. It is used against staphylococci that produce beta-lactamase, due to its large R chain, which does not allow the beta-lactamases to bind.

A steroid is a type of organic compound that contains a specific arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone.

Cresyl violet is an organic compound with the chemical formula C₁₉H₁₈ClN₃O. It is used in biology and medicine as a histological stain. Cresyl violet is an effective and reliable stain used for light microscopy sections.

Cilostazol is a medication used in the alleviation of the symptom of intermittent claudication in individuals with peripheral vascular disease.

Collagen is a group of naturally occurring proteins found, in nature, exclusively in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content.

Cobalamin, is a water soluble vitamin with a key role in the normal functioning of  brain and nervous system, and for the formation of blood. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid synthesis and energy production.

Coniine is a poisonous alkaloid found in poison hemlock and the yellow pitcher plant, and contributes to hemlock's fetid smell. It is a neurotoxin which disrupts the peripheral nervous system. It is toxic to humans and all classes of livestock.

Cumene is the common name for isopropylbenzene, an organic compound that is an aromatic hydrocarbon. It is a constituent of crude oil and refined fuels. It is a flammable colourless liquid that has a boiling point of 152 °C.

2-Cyanoguanidine is a nitrile derived from guanidine. It is a dimer of cyanamide, from which it can be prepared. 2-Cyanoguanidine is a colourless solid that is soluble in water, acetone, and alcohol, but not in diethyl ether or chloroform.

Cyclopentane is used in the manufacture of synthetic resins and rubber adhesives and also as a blowing agent in the manufacture of polyurethane insulating foam, as found in many domestic appliances such as refrigerators and freezers, replacing environmentally damaging alternatives such as CFC-11 and HCFC-141b.

1,4-Cyclohexadiene is a highly flammable cycloalkene that occurs as a colourless clear liquid. 1,4-Cyclohexadiene and related compounds may be prepared from benzene using lithium or sodium in liquid ammonia, this process being known as a Birch reduction.

Cyclododecane is an organic compound with the chemical formula C₁₂H₂₄. Cyclododecane is mainly used as an intermediate in production of flame retardants, detergents, and other chemicals.