GLOSSARY

A

Absolute configuration

The spatial arrangement of the atoms comprising a chiral molecule or group. More details here.

Achiral

Not chiral.

Amino acid dating

Anomalous x-ray scattering

A definitive technique for determining absolute configuration.

Asymmetric/asymmetrical

Not symmetric/not symmetrical.

Asymmetric carbon

A carbon atom bonded to four different types of atom or groups of atom. More details here.

B

Biological homochirality

The empirical observation that the molecular building blocks of life show consistent preferences for one chirality over the other; L amino acids rather than D amino acids, D sugars rather than L sugars etc.

c

Cahn-Ingold-Prelog priority rules

A convention for ascribing either an "(S)" descriptor or an "(R)" descriptor to an asymmetric carbon. More details here.

Circular birefringence

A difference in refraction for left- and right-handed circularly polarised electromagnetic waves (eg visible light). An example of optical activity. Gives rise to optical rotation.

Circular dichroism

A difference in absorption for left- and right-handed circularly polarised electromagnetic waves (eg visible light). An example of optical activity.

Circular differential photoacoustic spectroscopy

Circular polarisation of luminescence

Circular dichroism manifest in spontaneous emission rather than absorption.

Chiral/chirality

An entity is said to be "chiral" and have "chirality" if it differs from its mirror-image form. Derived from the Greek word for hand. Coined by Lord Kelvin.

Chiral rotational spectroscopy

A hybrid optical/microwave spectroscopic technique for chiral molecules.

Chiroptical (technique)

An optical technique with chiral sensitivity, eg optical rotation.

Cotton effect

The anomalous optical rotatory dispersion and circular dichroism seen together near an absorption resonance.

CRS

Stands for "chiral rotational spectroscopy".

D

Dextro rotatory

Clockwise optical rotation as seen when looking towards light source, ie positive specific rotation. See also laevo rotatory.

e

Enantiomer

One of a pair of distinct mirror-image objects. Usually 'small'; a chiral molecule, for example.

Enantiomorph

One of a pair of distinct mirror-image objects. Usually 'large'; a chiral crystal, for example.

Enantiomeric excess

A measure of the relative numbers of enantiomers in a sample. See here for more details.

Enantiomorphic excess

Analogous to enantiomeric excess but for 'large' chiral objects rather than 'small' ones. Used by Cameron in ICOA.

f

Faraday effect

Synonymous with Faraday rotation.

Faraday rotation

Optical rotation induced by a static magnetic field. See here for more details.

Fluorescence detected circular dichroism

The indirect measurement of circular dichroism via a corresponding difference in fluorescence intensities excited by left- and right-handed circular polarisations of light. Useful for samples with poor transmission, eg biological samples.

g

Gyrotropy

A synonym of optical activity?

H

Helicity

The projection of a particle's spin along the particle's direction of motion.

Heterochely

The projection of a particle's spin along the particle's direction of motion.

Hyper Rayleigh optical activity

Blah.

I

ICOA

An acronym for "interference-contrast optical activity".

ICOA-OR

An acronym for "interference-contrast optical activity", as applied to the measurement of optical rotation.

ICOA-GOR

An acronym for "interference-contrast optical activity", as applied to the measurement of optical rotation gradients.

ij infra zilches

A set of conserved properties of the free electromagnetic field. First described in (Cameron12a).

J

Jeremy (the lefty snail)

A garden snail with a shell that coiled to the left rather than to the right.

K

Kuhn dissymmetry factor (or ratio)

A measure of circular dichroism.

L

Laevo rotatory

Anticlockwise optical rotation as seen when looking towards source of light, ie negative specific rotation. See also dextro rotatory.

M

Magnetic optical rotation

Synonymous with the Faraday effect.

Magnetic circular dichroism

Differential absorption of left- and right-handed circular polarisations of light induced by a a static magnetic field. A manifestation of optical activity.

"M" descriptor

Used to describe the absolute configuration of a chiral molecule with an apparent left-handed helical structure. The "M" stands for "minus". See also "P" descriptor.

N

N

N.

O

OAM

Stands for "optical angular momentum" or "orbital angular momentum", usually in the form of helical phase fronts.

 

Octant rule

Used to interpret the signs and magnitudes of the Cotton effects induced in a chirally perturbed carbonyl chromophore.

Optical activity

A difference in response to left- and right-handed circular polarisations of light.

Optical rotation

The rotation of the azimuth of polarised light. Exhibited naturally by chiral samples and certain achiral anisotropic samples. Can be induced in all samples by a magnetic field; see the Faraday effect.

Optical rotatory dispersion

The variation of optical rotation as a function of frequency (or wavelength).

ORD

An acronym for "optical rotatory dispersion".

P

"P" descriptor

Used to describe the absolute configuration of a chiral molecule with an apparent right-handed helical structure. The "P" stands for "plus". See also "M" descriptor.

Polarimetry

The measurement of polarisation changes induced by a sample, eg optical rotation.

Q

Q

Q

R

Racemate

Racemization

"(R)" descriptor

One of two possible descriptors attributable to a chiral centre according to the Cahn-Ingold-Prelog priority rules; see also "(S)" descriptor. The "R" stands for "rectus". More details here.

S

"(S)" descriptor

One of two possible descriptors attributable to a chiral centre according to the Cahn-Ingold-Prelog priority rules; see also "(R)" descriptor. The "S" stands for "sinister". More details here.

Snapshot circular dichroism

A multiplexed approach towards the measurement of circular dichroism.

Specific ellipticity

The ellipticity induced by a sample due to circular dichroism (or circular extinction), normalised by density and path length.

Specific rotation (aka specific optical rotatory power)

The optical rotation induced by a sample, normalised by density and path length.

Specific optical rotatory power

A synonym of specific rotation.

T

Tyrian purple

The colour of a purple dye made using sea snails.

U

U

U

V

Verdet's law

The relationship between Faraday optical rotation, material properties embodied by the Verdet constant, magnetic field strength and the relative orientation of magnetic field and light propagation direction.

Vibrational optical activity

Optical activity deriving from the vibrational degrees of freedom of e.g. a chiral molecule. Examples of vibrational optical activity include VCD and ROA.

 

Vibrational circular dichroism

Is this a thing?

W

White-light polarimetry

The measurement of optical rotation using a continuous spectrum of visible (ie white) light. Described in (Anderson19).

X

X-ray scattering

The scattering of x-rays from e.g. the lattice planes of a crystal. Used with anomalous x-ray scattering to determine absolute configuration.

Y

YTILARIHC.COM

This lovely website. Note that "ytilarihc" is "chirality" spelled backwards.

Z

Zilch

A set of ten (nine independent) conserved properties of the electromagnetic field in vacuum, first described in (Lipkin64a). Higher-order versions of optical helicity, optical spin and the ij infra zilches, as explained in (Cameron12a).

REFERENCES

(Anderson19a) J Anderson, C Gillen, J Wright, C S Adams & I G Hughes 2019 Optical rotation of white light Am. J. Phys. 88 247-251

(Cameron12a) R P Cameron, S M Barnett & A M Yao 2012 Optical helicity, optical spin and related quantities in electromagnetic theory New J. Phys. 14 053050

(Lipkin64a) D M Lipkin 1964 Existence of a new conservation law in electromagnetic theory J. Math. Phys. 696-700

This website is funded by a grant from the Royal Society (URF\R1\191243)

Last updated: 15th of August 2020

Background: inverted Tyrian purple

© Dr Robert P Cameron MInstP 2020