The ring continually opens and closes, sometimes closing with one stereochemistry and sometimes with the other. Wavy single bonds represent unknown or unspecified stereochemistry or a mixture of isomers.
In this case the two possible ring structures are in chemical equilibrium with each other and also with the open-chain structure. Many solid chemical substances—for example many silicate minerals —are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to The structure of a chemical compound another in fixed ratios; even so, these crystalline substances are often called " non-stoichiometric compounds ".
Definitions[ edit ] Any substance consisting of two or more different types of atoms chemical elements in a fixed stoichiometric proportion can be termed a chemical compound; the concept is most readily understood when considering pure chemical substances.
Hydrogen atoms attached to atoms other than carbon must be written explicitly.
Solid wedged or dashed wedged bonds represent bonds pointing above-the-plane or below-the-plane of the paper, respectively. Unspecified stereochemistry[ edit ] Fructosewith a bond at the hydroxyl OH group upper left of image with unknown or unspecified stereochemistry. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: The presence of a positive or negative charge at a carbon atom takes the place of one of the implied hydrogen atoms.
In both cases, two specific carbon atoms and their connecting bond are the center of attention. The projection is totally unrealistic, as a saccharide would never adopt this multiply eclipsed conformation.
Newman projection of butane Cyclohexane conformations[ edit ] Certain conformations of cyclohexane and other small-ring compounds can be shown using a standard convention.
A solid wedged bond seen for example at the nitrogen N at top indicates a bond pointing above-the-plane, while a dashed wedged bond seen for example at the hydrogen H at bottom indicates a below-the-plane bond. Skeletal formulae can depict cis and trans isomers of alkenes. In the Newman projection, a circle is used to represent a plane perpendicular to the bond, distinguishing the substituents on the front carbon from the substituents on the back carbon.
There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require the fixed ratios.
It may be argued that they are related to, rather than being chemical compounds, insofar as the variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound, or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of the Earth.
Hydrogen atoms attached to carbon atoms are not indicated: In the sawhorse projection, the front carbon is usually on the left and is always slightly lower: Axial and equatorial positions are not distinguished; instead, substituents are positioned directly above or below the ring atom to which they are connected.
Chair conformation of beta-D-Glucose Haworth projection[ edit ] The Haworth projection is used for cyclic sugars. Chemical compounds can be molecular compounds held together by covalent bondssalts held together by ionic bondsintermetallic compounds held together by metallic bondsor the subset of chemical complexes that are held together by coordinate covalent bonds.
At any given carbon center, vertical bond lines are equivalent to stereochemical hashed markings, directed away from the observer, while horizontal lines are equivalent to wedges, pointing toward the observer.
Wavy single bonds are the standard way to represent unknown or unspecified stereochemistry or a mixture of isomers as with tetrahedral stereocenters. For example, the standard chair conformation of cyclohexane involves a perspective view from slightly above the average plane of the carbon atoms and indicates clearly which groups are axial and which are equatorial.
In the case of non-stoichiometric compoundsthe proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e. A crossed double-bond has been used sometimes, but is no longer considered an acceptable style for general use.
Stereochemistry in skeletal formulas[ edit ] Skeletal formula of strychnine. Hydrogen substituents are typically omitted.
Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly.
Chirality in skeletal formulas is indicated by the Natta projection method.The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged.
The chemical bonding within the molecule is also shown, either explicitly or implicitly. ChemSpider is a free chemical structure database providing fast access to over 34 million structures, properties and associated information.
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