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Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
What are the special features of the structure of graphene and how are the conducting properties of graphene/graphite explained? The honeycomb-shaped graphene is formed by hexagons of carbon atoms bonded together through sp2 hybrid bonds, resulting in interlocking hexagonal carbon rings. Each carbon atom has an extra electron, that is, one electron more than the number of atoms to which it is bonded. The outer-shell electrons of each carbon atom form three in-plane σ bonds and an out-of-plane π-bond (orbital). A σ-bond is the strongest type of covalent chemical bond. In a σ-bond, the electron pair occupies an orbital − a region of space associated with a particular value of the energy of the system − located mainly between the two atoms and symmetrically distributed about the line determined by their nuclei. A π-bond is a covalent bond where two lobes of one involved electron orbital overlap two lobes of the other involved electron orbital. It is a cohesive interaction between two atoms and a pair of electrons that occupy an orbital located in two regions, roughly parallel to the line determined by the two atoms. The out-of-plane π-orbital or electron is delocalized and distributed over the entire graphene plane. This freedom of movement of the electron makes graphene/graphite thermally and electrically conducting.
Alkenes and Alkynes: Structure, Nomenclature, and Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A π-bond is a covalent chemical bond formed by the overlap of two lobes of an orbital on one atom with two lobes of an orbital on an adjacent atom. What is the structure of ethene (the common name is ethylene)?
Chemicals from Paraffin Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
Ethylene is considered to be one of the most important raw materials in the chemical industry. Its significance is driven by its molecular structure, i.e., carbon-carbon double bonds (H2C=CH2). This π-bond is responsible for its chemical reactivity. The double bond is also a place of high electron density; therefore, it is susceptible to attack by electrophiles. It is a volatile substance, colorless at room temperature, noncorrosive, nontoxic, flammable gas, slightly soluble in water, and soluble in most organic solvents. It has boiling and melting points of −104°C and −169.2°C, respectively, at a pressure of 1 atm. Ethylene is a very active chemical; as exemplified by the reaction between ethylene and water to produce ethyl alcohol. Most of the ethylene reactions are catalyzed by transition metals, which bind transiently to the ethylene using both the π and π* orbitals. Ethylene is also an active alkylating agent, which can be used for the production of important monomers, such as ethyl benzene (EB), which is dehydrogenated to styrene.
Synthesis, characterisation and quantum chemical studies of a new series of iron chelatable fluorescent sensors
Published in Molecular Physics, 2019
Huihui Yan, Robert C. Hider, Yongmin Ma
The results presented in Table S2 and Figure 3 showed the interaction energies of all core and lone pair orbitals of molecule to anti-bonding orbitals. The most probable transition in 9c are π(C1–C2) → π*(C6–O7), π(C4–C5) → π*(C6–O7), π(C9–C10) → π*(C4–C5), π(C9–C10) → π*(C11–C12), π(C11–C12) → π*(C9–C10), π(C11–C12) → π*(C13–C14), π(C11–C12) → π*(C15–C16), π(C13–C14) → π*(C11–C12), π(C13–C14) → π*(C15–C16), π(C15–C16) → π*(C11–C12), π(C15–C16) → π*(C13–C14), LP1(N3) → π*(C1–C2), LP1(N3) → π*(C4–C5), LP1(O7) → RY*1(C6), LP2(O7) → σ*(C1–C6), LP2(O7) → σ*(C5–C6), LP2(O8) → π*(C1–C2), LP1(N17) → π*(C13–C14) with interaction energies 18.31, 27.7, 14.28, 11.13, 18.23, 18.44, 20.93, 23.59, 15.97, 15.57, 19.45, 33.08, 44.31, 12.28, 16.61, 17.69, 37.95 and 28.08 kcal/mol, respectively. From this, we can conclude that the transition among oxygen lone pair, nitrogen lone pair, and anti-bonding of π makes the state highly unstable. Combining the definition of fluorescent mechanism of molecule, high density of intramolecular electron conjugation is the main reason to generate fluorescence. The huge conjugated pi bond constituted by HPO moiety, carbon–carbon double bond moiety, benzene derivative moiety and the electron donor group (hydroxyl group and different nitrogenous groups) plays an important role to generate fluorescence.
Tribological characteristics of greases with and without metallo-organic friction-modifiers
Published in Tribology - Materials, Surfaces & Interfaces, 2018
Sujay Bagi, Kimaya Vyavhare, Pranesh B. Aswath
MoDTC is a well-known organomolybdenum friction modifier that has been used in the lubricants [35–37]. The friction reduction under boundary lubrication regime is attributed to the formation of MoS2 on the wear surface at asperity contacts [35–39]. However, pathways for tribochemical degradation of MoDTC to form MoS2 sheets are not clearly understood. MoS2 is a solid lubricant that has a hexagonal lamellar crystal structure wherein the layer’s slide on top of each other under loads leading to a reduction in the friction coefficient [40–44]. MoS2 structure is similar to graphite and thus shares a strong Mo-S covalent bond but a weak S-S pi bond in the inter-planar region of the crystal structure. This allows the sulphur bonds to break easily and the plane to shear off in order to form a tribofilms over the wear surface at the contact region. Studies have shown that ZDDP is synergistic with MoDTC in reducing wear and friction by forming MoS2 [45–48]. It was also reported that the issue of limited solubility of MoDTC in the lubricants could be overcome by mixing with organothiophosphates. Several analytical tools such as XPS (X-ray photoelectron spectroscopy), TEM (transmission electron microscopy) and Raman spectroscopy have been used in an attempt to understand the mechanism of MoS2 formation from MoDTC [49]. In this study, greases with single additive system were evaluated for wear and frictional performance for comparison to the greases with a mix of the additives, however, the mechanism of tribofilm formation with single additives is not addressed in this study as it has been studied extensively in previous studies [33,34].