conformation

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One of the very large number of possible spatial arrangements of atoms that can be interconverted by rotation about a single bond in a molecule. In the case of ethane, H₃C-CH₃, one methyl group can rotate relative to the other. There are two extreme cases. In one, the C-H bonds on one group align with the C-H bonds on the other (as viewed along the C-C bond). This is an eclipsed conformation (or eclipsing conformation) and corresponds to a maximum in a graph of potential energy against rotation angle. In the other the C-H bonds on one group bisect the angle between two C-H bonds on the other. This is a staggered conformation (or bisecting conformation) and corresponds to a minimum in the potential-energy curve. In the case of ethane, the energy difference between the two conformations is small (2.8 kcal/mole) and effective free rotation occurs under normal conditions.

In the case of butane, rotation can occur about the bond between the second and third carbon atoms, MeH₂C-CH₂Me. The highest maximum occurs when the methyl groups are eclipsed (they are at their closest). Maxima of lower energies occur when the methyl groups on one carbon atom eclipse the hydrogen atoms on the other. The lowest potential energy occurs when a C-Me bond bisects the angle between the C-H bonds (i.e. the two methyl groups are furthest apart). This is called the anti conformation. A lesser minimum occurs when the methyl group bisects the angle between a C-H bond and a C-Me bond. This arrangement is called the gauche conformation.

Similar rotational arrangements occur in other types of molecule. For instance, in a compound such as R₃C-CHO, with a C=O double bond, one conformation has the C=O bond bisecting the angle between C-R bonds. This is called the bisecting conformation (note that the C-H bond eclipses one of the C-R bonds in this case). The other has the C=O bond eclipsing a C-R bond. This is the eclipsed or eclipsing conformation. (In this case the C-H bond bisects the angle between the C-R bonds.)

See also torsion angle; ring conformations.

Conformations of butane (sawhorse projection)



Conformations of R₃CHO (Newman projection)

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noun

1. The act of making suitable to an end or the condition of being made suitable to an end: accommodation, adaptation, adaption, adjustment. See change/persist.
2. The act or state of agreeing or conforming: accordance, agreement, chime, conformance, conformity, congruence, congruity, correspondence, harmonization, harmony, keeping. See agree/disagree.

the various arrangements of the atoms of a molecule (of defined configuration) in space that differ only as after rotation about single bonds; the term is now sometimes extended to include rotation about π-bonds or bonds of partial order between one and two, and sometimes further extended to include also rotation about bonds of any order, including double bonds. Interconversion of molecules of different conformations does not involve the breaking and making of chemical bonds (except hydrogen bonds) or changes in chirality. The following special terms and symbols distinguish different possible conformations of various classes or portions of molecules.

• (1) Cyclic compounds. Nonplanar six-membered rings may exist in boat conformation, chair conformation, half-boat conformation, half-chair conformation, skew conformation (def. 1), or twist conformation (def. 1); and nonplanar five-membered rings may exist in envelope conformation or twist conformation (def. 2). For a six-membered or five-membered ring form of a monosaccharide or monosaccharide derivative these conformations may be designated by the following conformational descriptors suffixed to their chemical names:-B, boat;-C, chair;-E, envelope;-H, half-chair;-S, skew;-T, twist; the locants of the ring atoms that lie above and/or below the reference plane, when the numbering appears clockwise, may be added to these symbols as left superscripts and/or right subscripts, respectively. A bond to a tetrahedral atom in a six-membered ring is termed axial (abbr.: a) if it or its projection makes a large angle with the plane containing a majority of the ring atoms, and equatorial (abbr.: e) if this angle is small; the same terms are applied to atoms or groups attached to such bonds. The corresponding terms for a bond from an atom directly attached to a doubly bonded atom in a monounsaturated six-membered ring are pseudoaxial (abbr.: a′) and pseudoequatorial (abbr.: e′), respectively.
• (2) Nucleotides. When atom C-2′ or C-3′ of the ribo- or deoxyribofuranose ring of a nucleotide lies out of the plane of the other four ring atoms, the ring conformation is designated by the descriptor endo- if either atom lies above the ring, i.e. towards the nitrogenous base, and by the descriptor exo- if it lies below the ring, i.e. away from the base. In addition the base and sugar rings may be in either of two relative positions: the conformation is said to be anticlinal (abbr.: anti-) if the groups at positions 2 and 3 of a pyrimidine residue or positions 1, 2, and 6 of a purine residue lie away from the sugar ring, and synclinal (abbr.: syn-) if these groups lie over the sugar ring.
• (3) Torsion angle. If rotation about a given bond in a molecule is restricted for any reason, the conformation of atoms or groups about that bond may be described by the torsion angle (symbol: θ). When, in a Newman projection, two atoms or groups attached at opposite ends of a bond appear one more or less directly behind the other, i.e. θ≈ 0°, these atoms or groups are termed eclipsed, and that portion of the molecule is described as being in the eclipsed conformation. If not eclipsed (in an ideal case, when all torsion angles equal 60°), the atoms or groups are termed staggered, and the molecule is described as being in the staggered conformation; such a conformation is termed synperiplanar abbr.: sp) (or sometimes cis (abbr.: c)), synclinal abbr.: sc) (or sometimes gauche (abbr.: g) or skew), anticlinal (abbr.: ac), or antiperiplanar (abbr.: ap) (or sometimes trans (abbr.: t)) according as the torsion angle is, respectively, within ±30°, ±60°, ±120°, or ±180° of 0°, the torsion angle being defined according to specified criteria. (Note: Because the terms cis and trans have other meanings, their use in this context is not recommended.)

—conformational adj.

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Symmetry, size and shape of the various body regions relative to each other or the general appearance of the animal in terms of satisfying the observer's appreciation of what is a desirable appearance. Most breed societies issue lists of desirable and undesirable points of conformation. Most of them are desirable. Some are not and react adversely on the animals’ well-being. Desirable conformation may also be indicated by diagrams or photographs.
Also may refer to the spatial arrangement of atoms in a molecule.

• mitochondrial c. — mitochondria may be in an abnormal state of condensed conformation, detected by comparison with mitochondria of orthodox status; orthodox conformation is linked to inactive oxidase phosphorylation, condensed to active phosphorylation.

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Dansk (Danish)
n. - form, tilpasning, struktur

Nederlands (Dutch)
aanpassing, structuur

Français (French)
n. - (gén, Anat, Géol) conformation, (Chim) conformation

Deutsch (German)
n. - Anpassung, Gestalt(gebung)

Ελληνική (Greek)
n. - διαμόρφωση, σχηματισμός, συμμόρφωση

Italiano (Italian)
adattamento, struttura, conformazione

Português (Portuguese)
n. - conformação (f)

Русский (Russian)
структура

Español (Spanish)
n. - conformación, adaptación, ajuste, estructura

Svenska (Swedish)
n. - bildning, form, anpassning

中文（简体）(Chinese (Simplified))
构造, 调和的组成, 形态

中文（繁體）(Chinese (Traditional))
n. - 構造, 調和的組成, 形態

한국어 (Korean)
n. - 구조, 균형 잡힌 배치, 일치

日本語 (Japanese)
n. - 構造, 形態, 整合, 適合

العربيه (Arabic)
‏(الاسم) تكوين, تشكيل, تركيب‏

עברית (Hebrew)
n. - ‮מבנה, צורה, הסתגלות‬

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