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Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Alkynes - Acyclic branched or unbranched hydrocarbons having a carbon-carbon triple bond and the general formula CnH2n-2, RCCR'. Acyclic branched or unbranched hydrocarbons having more than one triple bond are known as alkadiynes, alkatriynes, etc. [5] Allotropy - The occurrence of an element in two or more crystalline forms. Allylic groups - The group CH2=CHCH2- (allyl) and derivatives formed by substitution. The term `allylic position' or `allylic site' refers to the saturated carbon atom. A group, such as OH, attached at an allylic site is sometimes described as "allylic". [5] Amagat volume unit - A non-SI unit previously used in high pressure science. It is defined as the molar volume of a real gas at one atmosphere pressure and 273.15 K. The approximate value is 22.4 L/mol. Amides - Derivatives of oxoacids R(C=O)(OH) in which the hydroxy group has been replaced by an amino or substituted amino group. [5] Amine oxides - Compounds derived from tertiary amines by the attachment of one oxygen atom to the nitrogen atom: R3N+O-. By extension the term includes the analogous derivatives of primary and secondary amines. [5] Amines - Compounds formally derived from ammonia by replacing one, two, or three hydrogen atoms by hydrocarbyl groups, and having the general structures RNH2 (primary amines), R2NH (secondary amines), R3N (tertiary amines). [5] Amino acids* - Compounds containing both a carboxylic acid group (-COOH) and an amino group (-NH2). The most important are the -amino acids, in which the -NH2 group in attached to the C atom adjacent to the -COOH group. In the -amino acids, there is an intervening carbon atom. [4] Ampere (A)* - The SI base unit of electric current. [1] Ampere's law - The defining equation for the magnetic induction B, viz., dF = Idl × B, where dF is the force produced by a current I flowing in an element of the conductor dl pointing in the direction of the current. Ångström (Å) - A unit of length used in spectroscopy, crystallography, and molecular structure, equal to 10-10 m. Angular momentum (L) - The angular momentum of a particle about a point is the vector product of the radius vector from this point to the particle and the momentum of the particle; i.e., L = r × p. [1] Angular velocity () - The angle through which a body rotates per unit time. Anilides - Compounds derived from oxoacids R(C=O)(OH) by replacing the -OH group by the -NHPh group or derivative formed by ring substitution. Also used for salts formed by replacement of a nitrogen-bound hydrogen of aniline by a metal. [5] Anion - A negatively charged atomic or molecular particle. Antiferroelectricity* - An effect analogous to antiferromagnetism in which electric dipoles in a crystal are ordered in two sublattices that are polarized in opposite directions, leading to zero net polarization. The effect vanishes above a critical temperature. Antiferromagnetism* - A type of magnetism in which the magnetic moments of atoms in a solid are ordered into two antiparallel aligned sublattices. Antiferromagnets are characterized by a zero or small positive magnetic susceptibility. The
Odd-even effects in liquid crystals
Published in Liquid Crystals, 2021
The odd–even behaviour for the alternative appearance of ferroelectricity and antiferroelectricity was observed in two homologous series of Pn-O-PIMB-(n – 2)* [10] and Pn-O-PIMB-(n-2)*-(n-4)O [11] type bent-core materials with molecular structures shown in Figure 2. In the molecular names, n stands for the number of carbons in each end chain and (n – 2)* for the chiral position from the oxygen next to the core; namely, the third carbon from the chain end (methyl carbon) is always chiral. Both types of molecules had showed antiferroelectric synclinic (SmCsPA*) phases for the odd-numbered homologs and ferroelectric anticlinic (SmCaPF*) phases for the even-numbered homologs.
Evidence of monotropic hexatic tilted smectic phase in the phase sequence of ferroelectric liquid crystal
Published in Phase Transitions, 2018
Anna Różycka, Aleksandra Deptuch, Teresa Jaworska-Gołąb, Dorota Węgłowska, Monika Marzec
Ferroelectric liquid crystals (FLCs) are known since 1974 when it was discovered by R.B. Meyer et al. [1], and from that time, a lot of theoretical and experimental works have been done concerning synthesis of new FLCs and study of their physical properties and potential applications. Later, antiferroelectricity was also discovered in liquid crystals [2]. At the beginning, they were interesting as physical phenomena – existence of ferroelectricity and antiferroelectricity in mesophases, while now ferroelectric and antiferroelectric liquid crystals are attractive from an application point of view. They can be used in liquid crystal display (LCD) as well as in non-display technologies, e.g. high-speed electro-optic devices for different photonic applications [3–5].
Mesomorphic properties of non-symmetric bent-core liquid crystals with a lateral substituent in the apex position
Published in Liquid Crystals, 2021
Helena Skopalová, Václav Kozmík, Michal Šmahel, Jiří Svoboda, Oliva Pacherová, Michal Kohout, Vladimíra Novotná
Bent-core liquid crystals have attracted broad interest in the past 20 years. Structure-property investigation (variation of the central cores, polar linkages, lateral substitution, terminal chains, etc.) of these materials revealed characteristic structural features influencing their mesomorphic properties and leading to versatile mesophases [1–4]. Similarly to other mesogenic compounds, bent-core liquid crystals exhibit mesophases identified as nematic, smectic and columnar. However, these mesophases typically possess unique character driven by the bent molecular structure [1,3]. Tilted smectic SmCP phases are probably the most frequent, with synclinic (S) or anticlinic (A) orientation of the tilt (corresponding indexes S or A at the letter C, respectively). The SmCP phases can exhibit ferroelectricity (F) or antiferroelectricity (A), with the polarisation vector P in neighbouring layers oriented in same direction for the F state or in the opposite direction for the A structure [1]. For SmCP polar phases, the tilting of the long axes occurs in a direction perpendicular to the layer polarisation, which leads to the layer chirality. However, there are bent-core mesophases with no preferential direction for the polar order. Eremin et al. [5] observed a paraelectric–antiferroelectric transition, described as the transition from conventional SmC to bent-core tilted SmCP phase. Their analysis was supported by NMR measurements showing a conformational change of the molecular tilt at the phase transition. On the other hand, there are several types of polar smectic A mesophases (denoted SmAP), with antiferroelectric character as well as with randomly distributed polar domains (SmAPR) [6,7]. Materials showing both the calamitic SmA phase and the polar bent-core mesophases were first reported by Kovalenko et al. [8].