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A common medicine used to relieve mild to moderate pain and reduce fever. Acetaminophen (N-acetyl-p-aminophenol), or paracetamol, is a white crystalline compound with the molecular formula C8H9NO2 (Fig. 1). It is a member of the aniline family of…

A member of a group of organic compounds that can be considered as derived from ammonia by replacement of one or more hydrogens by organic functional groups. Generally amines are bases of widely varying strengths, but a few that are acidic are…

An analytical technique for determining the composition of a sample in terms of the chemical elements present and their quantities or concentrations. Unlike other methods of elemental analysis, however, the sample is decomposed into its constituent…

A poisonous colorless, odorless, tasteless gas (CO), resulting from the incomplete combustion of carbon-containing materials. Carbon monoxide (Fig. 1) is an indoor hazard causing hundreds of deaths annually, and it is one of the six major air…

The attractive force that holds atoms or ions together. Chemical bonds are very strong. To break one bond in each molecule in a mole of material typically requires an energy of many tens of kilocalories.It is convenient to classify chemical bonding…

A chemical element, Cl, atomic number 17 and atomic weight 35.453. Chlorine exists as a greenish-yellow gas at ordinary temperatures and pressures (see illustration). It is second in reactivity only to fluorine among the halogen elements, and hence…

Typically, an aquatic vertebrate with scales, gills, and paired fins. Fishes (Fig. 1) are found throughout the world's waterways, from saltwater oceans to freshwater streams and ponds. About 35,000 species of fishes have been described to date. Many…

In thermodynamics, the amount of useful work that can be extracted from a closed thermodynamic system. The Helmholtz free energy applies to a process that takes place at a constant temperature T (isothermal process). The Gibbs free energy applies to…

A salt or ester of lactic acid (CH3CHOHCOOH). In lactates, the acidic hydrogen of the carboxyl group has been replaced by a metal or an organic radical. Lactates are optically active, with a chiral center at carbon 2. The two optical isomers of a…

An analytical technique for identification of chemical structures, determination of mixtures, and quantitative elemental analysis by measuring the mass-to-charge (m/z) ratio of ions produced when a sample is ionized. Determination of organic and…

A device that is capable of converting chemical energy into electrical energy with the use of whole bacterial cells as the catalyst. Fuels that are produced biologically are known as biofuels. Biofuel cells convert chemical energy from organic…

A chemical element, Os, atomic number 76, atomic weight 190.2. Osmium is a hard white metal of rare natural occurrence, and is usually found in nature alloyed with other platinum metals. Metal Periodic table Platinum The periodic table of the…

A two-component reaction involving the loss of electrons (oxidation) by one chemical species and the gain of electrons (reduction) by another; also known as a redox reaction. Both oxidation and reduction occur simultaneously and in equivalent…

The study of chemical changes resulting from the absorption of high-energy ionizing radiation. Such radiation includes alpha particles, electrons, gamma rays, fission fragments, protons, deuterons, helium nuclei, and heavier charged projectiles.…

One of the elements of atomic numbers 21–31, 39–49, and 71–81. The symbols of these elements, along with their atomic numbers and valence-shell electronic configurations, are given in Fig. 1. The elements are arranged in the order in which they…

A chemical obtained from wood. Woody plants comprise the greatest part of the organic materials produced by photosynthesis on a renewable basis. Replacement of fossil hydrocarbons, from which most organic chemicals are derived, is possible in many…

The scattering of x-rays by matter with accompanying variation in intensity for specific directions (or wavelengths) due to interference effects. X-ray diffraction is a powerful and readily available method for determining atomic arrangements in…

Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural…

A useful carbon-carbon bond-forming reaction in which aldehyde and alcohol functional groups are observed during the reaction. The aldol reaction was first reported by Aleksandr Porfiryevich Borodin, who observed the reaction using pentanal and…

A large aquatic reptile of the family Alligatoridae. Alligators belong to the family Alligatoridae in the reptilian order Crocodylia (Crocodilia). Common usage generally restricts the name alligator to the two extant species of the genus Alligator…

A small, tropical, evergreen tree (Pimenta dioica) and its dried, unripe fruit (berry). Allspice (Pimenta dioica; alternatively, P. officinalis) [see illustration] is a member of the myrtle family (Myrtaceae). Allspice, which is also known as…

Any protozoan moving by means of protoplasmic flow. In their entirety, ameboid protozoans (or ameboid protists) include naked amebas, those enclosed within a shell or test, and more highly developed representatives, such as heliozoians,…

One of the three living orders of the class Amphibia, encompassing the frogs and toads. Anura is the largest order of amphibians (class Amphibia), containing more than 7000 species of frogs (Fig. 1) and toads. Because members of the order Anura…

A natural order of the class Arachnida, commonly known as the spiders. Members of the order Araneae (also called Araneida)—the spiders (Fig. 1)—are widespread over most of the land areas of the world and are well adapted to many different habitats.…

Any vegetable that is prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North…

A chemical reaction or series of reactions leading to the predominant or exclusive formation of a single enantiomer, that is, one of an isomeric pair of chemical compounds whose molecules are nonsuperimposable mirror images. Enantiomers are said to…

An aromatic hydro­carbon, molecular formula C6H6, also know as benzol. Benzene is a clear, colorless, and flammable liquid which boils at 80.1°C and freezes at 5.5°C.Benzene (1) is an important chemical intermediate used to produce ethylbenzene…

An integrated device consisting of a biological recognition element and a transducer capable of detecting the biological reaction and converting it into a signal that can be processed. Ideally, the sensor should be self-contained, so that it is not…

The name for two species within the genus Bison of the cattle family Bovidae in the mammalian order Artiodactyla found in North America and Europe. Bison are artiodactyl mammals belonging to the genus Bison (family Bovidae). The North American bison…

A taxonomic order of insects comprising the cockroaches and termites. The order Blattodea, also referred to as Blattaria, contains at least 4500 species of cockroaches (Fig. 1) and 3000 species of termites. Previously, termites were assigned to a…

The name for several members of the family Bovidae in the mammalian order Artiodactyla. The buffalo is an Old World artiodactyl that resembles oxen in general appearance. The North American bison is often called a buffalo, but it is not related to…

Any terrestrial or aquatic animal that is capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows…

The measurement of the quantity of heat transferred during chemical reactions, changes of state, mixing of substances, as well as other chemical and physical processes. The unit of energy in the International System of Units is the joule, symbolized…

A member of the mammalian family Camelidae in the order Artiodactyla. Camels are even-toed, hoofed mammals (ungulates). There are three extant camel species: the Bactrian camel (Camelus bactrianus; Fig. 1), the wild Bactrian camel (C. ferus), and…

A medium-sized, spreading evergreen tree (Anacardium occidentale), which is grown widely in the tropics for its kidney-shaped edible nuts (also called cashews) and the resinous oil in the shells of the nuts. Cashew trees, which are native to Brazil,…

A class in the phylum Mollusca that is exclusively marine and includes squids, octopuses, and cuttlefishes. The molluscan class Cephalopoda is one of the major taxonomic groupings of marine animals and contains both extant members—squids (Fig. 1),…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

An order of the class Reptilia, including the turtles, terrapins, and tortoises; also termed Testudines. The order Chelonia (often referred to as Testudines) comprises one of the oldest groups of reptiles on Earth. Members of the Chelonia…

A branch of physical chemistry that seeks to explain time-dependent phenomena, such as energy transfer and chemical reaction, in terms of the detailed motion of the nuclei and electrons that constitute the system. As such, chemical dynamics seeks…

The common name for any of 25 species of rodents in the mammalian family Sciuridae. Chipmunks are assigned to three different genera within the mammalian family Sciuridae: Tamias, with 1 species; Eutamias, with 1 species; and Neotamias, with 23…

A white or colorless amorphous polysaccharide that forms a base for the hard outer integuments of crustaceans, insects, and other invertebrates. Chitin (see illustration) is an important nitrogenous polysaccharide that is found abundantly in nature.…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

An order of Insecta comprising the beetles. Beetles belong to the insect order Coleoptera. This is the largest animal order, containing approximately 400,000 species. With so many species, beetles show very great diversity in size, form, color,…

The common name used for the large aquatic reptiles included in the family Crocodylidae. Crocodile (see illustration) is the common name used to describe about 17 species of large aquatic reptiles assigned to the family Crocodylidae, which is one of…

An order of insects commonly known as earwigs, in reference to an unfounded superstition that they crawl into the ears of sleeping persons. Earwigs are elongate and flattened, with a pair of forceps-like appendages, or cerci, at the end of the…

An order of mammals comprising one family (Cynocephalidae), one genus (Cynocephalus), and two species—C. variegatus (Malayan colugo) and C. volans (Philippine colugo). These mammals inhabit the rainforests of Southeast Asia from the Malay Peninsula…

A cycloaddition reaction between a diene and a dienophile. The simplest Diels-Alder reaction (O. Diels and K. Alder, 1928) occurs between butadiene and ethylene and is often referred to as a [4+2] cycloaddition. The numbers, four and two in…

The transport of matter from one point to another by random molecular motions. Diffusion occurs in gases, liquids, and solids.Diffusion plays a key role in processes as diverse as permeation through membranes, evaporation of liquids, dyeing textile…

An order of the class Insecta comprising the true flies. Members of the order Diptera (class Insecta, phylum Arthropoda) are known as dipterans or flies (Fig. 1). The name Diptera is derived from the Greek di-ptera, for "two wings," because the…

Any member of the carnivorous mammalian family Canidae. All breeds of domestic dogs (Fig. 1), the wild dogs, and related species belong to the family Canidae. Despite the various breeds of domestic dogs that are known, the scientific name for all…