Accuracy

ch2=c=c=ch2    108 CH2=C=C=CH2

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    #  Species Formula
    98 PropaneC3H8
    99 Propane (Geo)C3H8
   100 Isopropyl lithiumH7LiC3
   101 Isopropyl lithium (Geo)H7LiC3
   102 Trimethyborane (Geo)H9BC3
   103 TrimethylboraneH9BC3
   104 Carbon, tetramerC4
   105 Diacetylene (Geo)C4H2
   106 DiacetyleneC4H2
   107 CH2=C=C=CH2 (Geo)C4H4
   108 CH2=C=C=CH2 C4H4
   109 Vinylacetylene (Geo)C4H4
   110 VinylacetyleneC4H4
   111 1,2-ButadieneC4H6
   112 1,3-ButadieneC4H6
   113 1-ButyneC4H6
   114 2-ButyneC4H6
   115 Bicyclobutane (Geo)C4H6
   116 BicyclobutaneC4H6
   117 2-Butyne (Geo)C4H6
   118 CyclobuteneC4H6


I.P.: 9.1 eV,     REF: R. D. Levin, S. G. Lias, "Ionization Potentials and Appearance Potential Measurements," 1971-1981, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand. 71, (1982), Cat. No. C13.48:71.
  
 PM7
CH2=C=C=CH2
 I=9.1 IR=LLNBS82
  H     0.00000000 +0    0.0000000 +0    0.0000000 +0     0     0     0
  C     1.08321850 +1    0.0000000 +0    0.0000000 +0     1     0     0
  C     1.30564579 +1  123.1022049 +1    0.0000000 +0     2     1     0
  C     1.27400513 +1  180.0000000 +0  178.8532840 +1     3     2     1
  C     1.30546970 +1  180.0000000 +0   -1.1474340 +1     4     3     1
  H     1.08300025 +1  123.3317772 +1   -0.0024609 +1     5     4     1
  H     1.08273313 +1  113.6082493 +1  179.9987453 +1     2     1     3
  H     1.08299895 +1  123.3368011 +1 -179.9996611 +1     5     4     6