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Linear Raman Spectroscopy
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Recall that chirality is a geometric property of (some) molecules, meaning that such a molecule is nonsuperposable on its mirror image. For example, the presence of an asymmetric carbon center is one of several structural features that are responsible for chirality in molecules. Note that left- and right-hand configurations of chiral molecules are often dubbed enantiomers. The left- and right-handed variants carry the labels S and R, respectively; they indicate the absolute configuration of the molecule; i.e., they refer to the actual orientation in space of the substituents around the stereo-center. This nomenclature allows one to describe the steric configuration of molecules, without the need for a 3D picture representation.
Inherent FR Fibers
Published in Asim Kumar Roy Choudhury, Flame Retardants for Textile Materials, 2020
Chirality is a geometric property of some molecules and ions. A chiral molecule/ion is non-superimposable on its mirror image. The presence of an asymmetric carbon center is one of several structural features that induce chirality in organic and inorganic molecules. The term chirality is derived from the Greek word for hand (Fox and Whitesel, 2004).
Organic Chemistry Nomenclature
Published in Arthur W. Hounslow, Water Quality Data, 2018
An asymmetric carbon atom is a carbon atom that has four different atoms or groups of atoms attached to it. The molecule is NOT identical to its mirror image. The result is optical isomerism, whereby one isomer rotates the vibration direction of polarized light to the left, and the other isomer rotates it to the right.
New chiral liquid crystal cyclic monomers based on diosgenin: synthesis and mesomorphism
Published in Liquid Crystals, 2018
Zhihao Guo, Pan Li, Xiaofeng Liu, Liqun Yang, Jianshe Hu, Zhangpei Chen
Chiral LC materials have been widely studied due to their excellent optical-electric properties, such as selective reflection of circular polarised light, high optical rotatory power, circular dichroism, thermochromism, ferroelectricity and piezoelectricity [13]. In general, the molecular structure of chiral LCs is formed by a spiral twisted structure containing one or more asymmetric carbon atoms. Due to the special spiral helical structure, chiral LCs have distinctive optical properties and can produce a chiral smectic C or cholesteric phases, which makes them candidates for important potential applications in flat-panel displays, thermal imaging, non-linear optical devices, rewritable full colour image recording and photostable UV screens [14–21]. In fact, LC compounds are also useful in bio-related fields because their self-organising structures through non-covalent specific interactions are compatible with those in living systems [22–26]. Furthermore, LC compounds can produce response through the self-assembling ability under external stimuli, such as temperature, pressure and electromagnetic fields. Because of their specific effect, steroidal compounds play important roles in the functions of biological system and LC soft matter, so they have become an interesting component with bioactivity. As a natural chiral mesogenic steroidal compound, diosgenin has become an attractive candidate to synthesise new smart, responsive and biodegradable LC materials.
NMR spectra of chiral smectic liquid crystals differing in helical parameters
Published in Liquid Crystals, 2018
Marzena Tykarska, Anna Drzewicz, Mateusz Szala, Magdalena Żurowska
The change of helix handedness for the same substance can be observed during the transition from one liquid crystalline phase to another [8,9] or within one phase [10–12]. The change of helical twist sense within one phase has different reason than described by theory of Gray and McDonnell [13]. According to this theory, the helical twist sense depends on the type of absolute configuration of asymmetric carbon atom and its position related to the rigid core of molecule. In the case of one compound the structure of chiral centre does not change. Thus another explanation has been proposed, namely the effect of inversion within one phase may be caused by the presence of different conformers promoting opposite handedness, which concentration may change with temperature [14–16].
Sign reversal of the spontaneous and induced polarisation in a mixture of achiral liquid crystal host and chiral azo dopant
Published in Liquid Crystals, 2023
Osamu Tsutsumi, Makoto Nakano, Gurumurthy Hegde, Lachezar Komitov
In this study, an azobenzene derivative with asymmetric carbon atoms was newly designed and synthesised as a photochromic chiral azo dopant. The molecular structure and synthetic route for the azo dopant are shown in Figure 3. We prepared the azo dopant from hydroquinone by a nine-step synthetic route containing a nucleophilic substitution of optically active 2-bromopropionic acid and a diazo coupling reaction. The dopant was successfully purified by column chromatography, followed by recrystallisation. It was fully characterised by spectroscopies, and all analytical data confirm that the desired compound was obtained.