GaucheKonformation

GaucheKonformation, often written as gauche conformation or Gauche-Konformation in German literature, refers to a specific arrangement of substituents around a single carbon–carbon bond in organic molecules. It is one of the staggered conformations, distinguished from the anti arrangement by the dihedral angle between the substituents on adjacent atoms.

In a Newman projection, a gauche conformation shows the two substituents offset by about 60 degrees rather than being directly opposite each other (180 degrees, the anti form). This arrangement places some steric interaction between the substituents, typically resulting in a higher energy state compared with the anti conformation. A classic example is butane, in which the two methyl groups can adopt a gauche orientation relative to one another. The gauche form is less stable than the anti form, with a small energetic penalty on the order of about 0.9 kcal/mol (roughly 3–4 kJ/mol).

Gauche interactions are a general feature of conformational analysis and can influence physical properties such as conformer populations, boiling points, and reactivity. In cyclic or constrained systems, gauche relationships can arise because anti arrangements are geometrically inaccessible. In some fluorinated and electronegative systems, a broader “gauche effect” can stabilize gauche conformations through electronic factors like hyperconjugation and dipole interactions, sometimes counteracting steric expectations.

See also: dihedral angle, Newman projection, staggered vs eclipsed conformations, anti conformation, gauche effect.