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Shorter than average C–C bond distances are also possible: alkenes and alkynes have bond lengths of respectively 133 and 120 pm due to increased s-character of the sigma bond. In benzene all bonds have the same length: 139 pm. Carbon–carbon single bonds increased s-character is also notable in the central bond of diacetylene (137 pm) and ...
Comparison of bond lengths in simple hydrocarbons [5] Molecule Ethane: Ethylene: Acetylene: Formula C 2 H 6: C 2 H 4: C 2 H 2: Class alkane: alkene: alkyne: Structure Hybridisation of carbon sp 3: sp 2: sp C-C bond length 153.5 pm: 133.9 pm: 120.3 pm: Proportion of C-C single bond 100% 87% 78% Structure determination method microwave ...
An example is Bragg's 1921 classical paper on the structure of ice, [11] which gives the c- and a-axis lattice constants as 4.52 A.U. and 7.34 A.U., respectively. Ambiguously, the abbreviation "a.u." may also refer to the atomic unit of length, the bohr—about 0.53 Å—or the much larger astronomical unit (about 1.5 × 10 11 m). [27] [28] [29]
In solid materials, the atomic spacing is described by the bond lengths of its atoms. In ordered solids, the atomic spacing between two bonded atoms is generally around a few ångströms (Å), which is on the order of 10 −10 meters (see Lattice constant ).
For example, in the phenylpropyne complex Pt(PPh 3) 2 (MeC 2 Ph), the C-C distance is 1.277(25) vs 1.20 Å for a typical alkyne. The C-C-C angle distorts 40° from linearity upon complexation. [ 4 ] Because the bending induced by complexation, strained alkynes such as cycloheptyne and cyclooctyne are stabilized by complexation.
The covalent radius, r cov, is a measure of the size of an atom that forms part of one covalent bond. It is usually measured either in picometres (pm) or angstroms (Å), with 1 Å = 100 pm. In principle, the sum of the two covalent radii should equal the covalent bond length between two atoms, R(AB) = r(A) + r(B).
As a rule of thumb, R free should be approximately the resolution in angstroms divided by 10; thus, a data-set with 2 Å resolution should yield a final R free ~ 0.2. Chemical bonding features such as stereochemistry, hydrogen bonding and distribution of bond lengths and angles are complementary measures of the model quality.
The micrometre (SI symbol: μm) is a unit of length in the metric system equal to 10 −6 metres ( 1 / 1 000 000 m = 0. 000 001 m). To help compare different orders of magnitude , this section lists some items with lengths between 10 −6 and 10 −5 m (between 1 and 10 micrometers , or μm).