Ethyne bond length

Measure and record the carbon-carbon bond lengths in ethane, ethene and ethyne. These will serve as standards for single, double and triple bonds, respectively. 

A well-known example of the effect of bond order on bond length is provided by the bonds in ethane, ethene, and ethyne, which have the lengths of 154, 134, and 120 pm, respectively. Covalent radii for doubly and triply bonded atoms can be obtained from double and triple bond lengths in the same way as for single bonds. Some values are given in Table 2.2. 

Figure 1.30 Bond angles and bond lengths of ethyne, ethene, and ethane.

Ethyne, ethene and ethane contain 10. 12 and 14 valence electrons, respectively. They are isoelectronic with N2, 02 and F., respectively. Along both series of molecules the central link becomes progressively weaker and the bond lengths increase. The carbon-carbon bond length increases from 121 pm in ethyne to 133 pm in ethene and to 155 pm in ethane. The corresponding bond enthalpy terms are 837, 612 and 348 kJ mol Data for the diatomic molecules is contained in the text. Discuss these data in terms of the VSEPR and MO treatments of the molecules. 

The CsC triple bonds of other alkynes closely follow the same pattern as ethyne including the effect of the extra QC methods. Since QC results have been collected for a significant number of compounds with C=C triple bonds and since they all show that MP2 calculations give rather poor bond lengths while the B3LYP model consistently gives bond lengths closer to experimental whether r, tq or even r, these results are presented in a different format in Table lOA for only a few combinations of method and basis set. 

Ethylidyne (8) has been recognised on Pt/SiOa at 300 K using the SEDOR NMR technique applied to heavily C-labelled ethene the C—C bond length was 149 pm. This seemed to occur on large platinum particles, where areas of (111) face are most likely it was also seen by SIMS on platinum black, but on small particles vinylidene (17) predominated. Similar SEDOR experiments with ethyne showed 75% vinylidene and 25% ethyne as 12A or 15. " Adsorbed benzene was shown to rotate freely at 300 K, and cyclopropane was adsorbed, but not strongly, i.e. without loss of hydrogen. ... 

Based on the data in Model 1 for ethane, ethene, and ethyne, what is the relationship between bond order and bond length ... 

The carbon—carbon triple bond of ethyne is shorter than the carbon—carbon double bond of ethene, which in turn is shorter than the carbon—carbon single bond of ethane. The reason is that bond lengths are affected by the hybridization states of the carbon atoms involved. 

Reaction of bis(cyclopentadienyl)diphenyltitanium(iv) with acetylenes affords a general route to titana-indenes. The products from the reactions with phenyl-(trimethylsilyl)ethyne and bis(pentafluorophenyl)ethyne were both characterized by single crystal Z-ray studies, and the structure of the former is shown in (6). The structure is drawn with the one double bond, because, unlike metallocyclo-pentadienes in general, the Ci—Ca bond in (6) is significantly shorter than C3—C4, which is typically aromatic. The two Ti—C bonds in (6) are similar in length but the Ti—Cx bond length in the pentafluorophenyl compound is longer, which the authors attribute to steric factors. ... 

The length of a bond between a carbon atom and another atom is the shortest for a carbon atom with sp hybrid orbitals. The carbon-hydrogen bond lengths for ethyne, ethene, and ethane are 105, 109, and 111 pm, respectively. The C—H bond energy of ethyne is 536 kj moleA larger than the 470 kJ mole C—H bond energy of ethene and the 422 kJ mole" C—H bond energy of ethane. 

Answer Since the sp -sp bond length in ethene is 105 pm and the sp—sp bond length in ethyne is 109 pm, based on hybridization effects... 

Another type of unsaturated hydrocarbon, called an alkyne, contains a triple bond between two carbon atoms. Alkynes are named using the alkane root name for a given carbon chain length and changing the -ane ending to -yne. Ethyne, known more commonly as acetylene, is the most important commercial alkyne. Most acetylene produced in the United States is used to make vinyl and acrylic materials, although about ten percent is burned in oxyacetylene torches. These torches are used to cut and weld metals. Few alkynes are known to occur naturally because they are very reactive. However, they can be synthesized from other organic compounds. The names and structures of some small alkyne molecules are shown in Table 18.2. 

Table 1.7 Comparison of the Bond Angles and the Lengths and Strengths of the Carbon-Carbon and Carbon-Hydrogen Bonds in Ethane, Ethene, and Ethyne...

Structures for ethyne based on calculated molecular orbitals and electron density are shown in Fig. 1.31. Circular symmetry exists along the length of a triple bond (Fig. 1.31 ). As a result, there is no restriction of rotation for groups joined by a triple bond (as compared with alkenes), and if rotation would occur, no new compound would form. 

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