China
Africa
Explore chapters and articles related to this topic
Reduction Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Each covalent bond requires that a certain amount of energy be added to break it. That same amount of energy is inherent to the bond and is called the bond dissociation energy. When a carbon–carbon double bond is broken during catalytic hydrogenation, the bond dissociation energy for that bond is released and is called heat of hydrogenation (alternatively, the amount of heat that must be added to disrupt the C=C bond). What information does heat of hydrogenation provide about alkenes?
Thermochemistry (Following)—Heats of Reactions and Bond Energies
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
Firstly, it is necessary to distinguish the notions of bond energy and of bond dissociation energy. The bond dissociation energy refers to the energy required to break a given bond of a specific compound.The bond energy is an average value of the bond dissociation energies of a given bond in a series of different compounds possessing the same bond. (The obtained value may have suffered from a few small adjustments for the purpose of matching a great deal of data).
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
Diazo compounds - Compounds having the divalent diazo group, =N+=N-, attached to a carbon atom, e.g., CH2=N2 diazomethane. [5] Dielectric constant ()* - Ratio of the electric displacement in a medium to the electric field strength. Also called permittivity. [1] Dienes - Compounds that contain two fixed double bonds (usually assumed to be between carbon atoms). Dienes in which the two double-bond units are linked by one single bond are termed conjugated. [5] Differential scanning calorimetry (DSC) - See Techniques for Materials Characterization, page 12-1. Differential thermal analysis (DTA) - See Techniques for Materials Characterization, page 12-1. Diffusion* - The migration of atoms, molecules, ions, or other particles as a result of some type of gradient (concentration, temperature, etc.). Diopter - A unit used in optics, formally equal to m-1. It is used in expressing dioptic power, which is the reciprocal of the focal length of a lens. Dipole moment, electric (p,µ)* - For a distribution of equal positive and negative charge, the magnitude of the dipole moment vector is the positive charge multiplied by the distance between the centers of positive and negative charge distribution. The direction is given by the line from the center of negative charge to the center of positive charge. Dipole moment, magnetic (m,µ) - Formally defined in electromagnetic theory as a vector quantity whose vector product with the magnetic flux density equals the torque. The magnetic dipole generated by a current I flowing in a small loop of area A has a magnetic moment of magnitude IA. In atomic and nuclear physics, a magnetic moment is associated with the angular momentum of a particle; e.g., an electron with orbital angular momentum l exhibits a magnetic moment of -el/2me where e is the elementary charge and me the mass of the electron. [1] Disaccharides - Compounds in which two monosaccharides are joined by a glycosidic bond. [5] Dislocation - An extended displacement of a crystal from a regular lattice. An edge dislocation results when one portion of the crystal has partially slipped with respect to the other, resulting in an extra plane of atoms extending through part of the crystal. A screw dislocation transforms successive atomic planes into the surface of a helix. Dispersion - Splitting of a beam of light (or other electromagnetic radiation) of mixed wavelengths into the constituent wavelengths as a result of the variation of refractive index of the medium with wavelength. Dissociation constant* - The equilibrium constant for a chemical reaction in which a compound dissociates into its constituent parts. Dissociation energy (De)* - For a diatomic molecule, the difference between the energies of the free atoms at rest and the minimum in the potential energy curve. The term bond dissociation energy (D0), which can be applied to polyatomic molecules as well, is used for the difference between the energies of the fragments resulting when a bond is broken and the energy of the original molecule in its lowest energy state. The term bond strength implies differences in enthalpy rather than energy.
Thermal stability and detonation characters of nitro-substituted derivatives of pyrazole
Published in Molecular Physics, 2020
Bu-Tong Li, Lu-Lin Li, Lin-Li Liu
The strength of the covalent bond can be represented by the bond dissociation energy (BDE). In theory, BDE of the bond A−B can be calculated according to the enthalpy change of the hemolysis reaction . So, BDE can be obtained based on the following equation: in which is the BDE of A−B; , and are the total energy of molecule AB, the radical A·, and the radical B·, respectively.
Substituted hydrocarbon: a CCSD(T) and local vibrational mode investigation
Published in Molecular Physics, 2021
Alexis Antoinette Ann Delgado, Daniel Sethio, Devin Matthews, Vytor Oliveira, Elfi Kraka
Despite the many investigations conducted on substituted hydrocarbon systems, there has been no quantitative assessment involving a reliable bond strength parameter to evaluate the effect substituents have on the intrinsic bond strength of carbon–carbon bonds. Bond dissociation energy (BDE) is used to quantify the strength of chemical bonds because it is interpreted as a measure of bond energy. Cremer and co-workers demonstrated that the BDE is inadequate for determining molecular intrinsic bond strengths in cases beyond diatomic molecules because the stabilisation energy includes the electronic reorganisation and geometrical relaxation of the fragments [70]. In addition to BDE, vibrational frequencies [71], bond (electron) density [69,72], and bond length [34,73] have been shown to be inadequate descriptors of bond strength. Moreover, previous work showed a good correlation between CC bond lengths and electron densities at the bond critical point (BCP) for ethane and derivatives [74,75]; but for substituted systems of acetylene and ethylene, a poor correlation was analysed [34]. The local mode force constant , obtained through the local vibrational mode analysis (defined as LVMA below) originally introduced by Konkoli and Cremer [71,76–78], effectively probes the intrinsic strength of a bond/weak interaction [79] as this quantitative measure does not require bonds/interactions to be dissociated which allows the geometry and electronic structure of a bond to be preserved. The local mode force constant has been successfully used to systematically investigate the strength of single and multiple covalent bonds of the following: C [80], mono-substituted benzenes [81], carbon-halogen bonds [82,83], and ultra-long C−C bonds [84,85].