Term: helicity
https://doi.org/10.1351/goldbook.H02763

Definition:
The chirality of a helical, propeller or screw-shaped molecular entity. A right-handed helix is described as P (or plus), a left-handed one as M (or minus). H02763-1.png H02763-2.png  The application of this system to the description of conformations considers the torsion angle between two specified (fiducial) groups that are attached to the atoms linked by that bond. The sign of the smaller torsion angle between the fiducial groups defines the chirality sense of the helix. Rules for the selection of fiducial groups according to priority are given by R.S. Cahn, C.K. Ingold and V. Prelog, Angew. Chem. 78, 413-447 (1966), Angew. Chem. Internat. Ed. Eng. 5, 385-415, 511 (1966).

Related Terms:
1) axial chirality (http://doi.org/10.1351/goldbook.A00547).
2) Δ (delta), Λ (lambda) (http://doi.org/10.1351/goldbook.D01511).
3) chirality (http://doi.org/10.1351/goldbook.C01058).
4) torsion angle (http://doi.org/10.1351/goldbook.T06406).
5) helix (http://doi.org/10.1351/goldbook.H02769).
6) chirality sense (http://doi.org/10.1351/goldbook.C01063).
7) priority (http://doi.org/10.1351/goldbook.P04854).

Images:
1) Not defined (https://goldbook.iupac.org/img/inline/H02763-1.png) 
2) Not defined (https://goldbook.iupac.org/img/inline/H02763-2.png) 

Source: PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2209 (https://doi.org/10.1351/pac199668122193)

Citation: 'helicity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.H02763

License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.

Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.