For example, chlorination and bromination of naphthalene proceeds without a catalyst to give 1-chloronaphthalene and 1-bromonaphthalene, respectively. In electrophilic aromatic substitution reactions, naphthalene reacts more readily than benzene. Chemical properties Reactions with electrophiles However, the solid shows semiconducting character below 100 K. Both in the liquid and in the solid, the resistivity depends on temperature as ρ = ρ 0 exp( E/( k T)), where ρ 0 (Ω m) and E (eV) are constant parameters, k is Boltzmann's constant (8.617×10 −5 eV/ K), and T is absolute temperature (K). The resistivity drops more than a thousandfold on melting, to about 4 × 10 8 Ω m. Pure crystalline naphthalene is a moderate insulator at room temperature, with resistivity of about 10 12 Ω m. The point group symmetry of naphthalene is D 2h. Bicyclodecapentaene is a structural isomer with a fused 4–8 ring system and azulene is another, with a fused 5-7 ring system. Two isomers are then possible for mono-substituted naphthalenes, corresponding to substitution at an alpha or beta position. Thus there are two sets of equivalent hydrogen atoms: the alpha positions, numbered 1, 4, 5, and 8, and the beta positions, 2, 3, 6, and 7.
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This theorem would describe naphthalene as an aromatic benzene unit bonded to a diene but not extensively conjugated to it (at least in the ground state), which is consistent with two of its three resonance structures.īecause of this resonance, the molecule has bilateral symmetry across the plane of the shared carbon pair, as well as across the plane that bisects bonds C2-C3 and C6-C7, and across the plane of the carbon atoms. This difference, established by X-ray diffraction, is consistent with the valence bond model in naphthalene and in particular, with the theorem of cross-conjugation. The bonds C1−C2, C3−C4, C5−C6 and C7−C8 are about 1.37 Å (137 pm) in length, whereas the other carbon–carbon bonds are about 1.42 Å (142 pm) long. Unlike benzene, the carbon–carbon bonds in naphthalene are not of the same length. The shared carbons are labeled 4a (between 4 and 5) and 8a (between 8 and 1).
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For purpose of the standard IUPAC nomenclature of derived compounds, those eight atoms are numbered 1 through 8 in sequence around the perimeter of the molecule, starting with a carbon adjacent to a shared one. The eight carbons that are not shared by the two rings carry one hydrogen atom each. (In organic chemistry, rings are fused if they share two or more atoms.) As such, naphthalene is classified as a benzenoid polycyclic aromatic hydrocarbon (PAH). Physical properties Ī naphthalene molecule can be viewed as the fusion of a pair of benzene rings. The structure of two fused benzene rings was proposed by Emil Erlenmeyer in 1866, and confirmed by Carl Gräbe three years later. Naphthalene's chemical formula was determined by Michael Faraday in 1826. He proposed the name naphthaline, as it had been derived from a kind of naphtha (a broad term encompassing any volatile, flammable liquid hydrocarbon mixture, including coal tar).
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In 1821, John Kidd cited these two disclosures and then described many of this substance's properties and the means of its production. In the early 1820s, two separate reports described a white solid with a pungent odor derived from the distillation of coal tar.