Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: craken66 on August 28, 2014, 10:03:47 AM
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Hello,
I'm writing to ask how chloride materials, for instance chloroform, are light-sensitive, especially SUN light. Why the Cl-C (or P) bond decomposes? Don't hesitate to post your opinions. Thank you~
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What are C-Cl or Cl-P bond enthalpies versus, say, C-H?
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What are C-Cl or Cl-P bond enthalpies versus, say, C-H?
I searched for the bond energy and others as follows.
C-Cl bond dissociation energy is 328 kJ/mol, and C-N bond energy(293) smaller than C-Cl. Dose it mean C-N bond is more light-sensitive?
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Using bond disassociation energy, that would mean that the C-N bond is more reactive then the C-Cl bond. Maybe that explains all the N2 in the atmosphere...
As far as the Uv (sun light) goes, its because the photons are hitting the bond in a deconstructive way, which would in turn split the bond and give radicals. Which does happen in radical organic chemistry, as well as, when you use molecular orbital theory.
Actually, now thinking more about it I cant rememeber if it's deconstructive or constructive interference that occurs, although deconstructive makes more sense and would agree with the molecular orbital approach.
Hope this helps!
8)
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Wiki always at hand
http://en.wikipedia.org/wiki/Bond-dissociation_energy
The discussion drifted from C-H to C-N, why? Then with wrong data and wrong deductions...
3.43eV for C-Cl is well within reach of sunlight, that's 361nm or near UV. 4.25eV for C-H would be less accessible at 292nm.
More important: the C-Cl bond is polarized, hence sensitive to light. C-H far less so.
An other difference is that C-Cl has an elongation mode at a much lower frequency that C-H, because Cl is heavier, and this may provide a path for multi-photon dissociation.
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How does polarized mean sensitive to light?
Using that same thinking you would expect H2O to be sensitive to light also, which I'm fairly sure is not.