Explanation for bond lengths in trans-hexatriene
Hexatriene is an unsaturated hydrocarbon with six carbon atoms and five carbon-carbon bonds, three of which are double bonds.
However, the bond lengths of the $ce{C=C}$ bonds are not the same. The middle $ce{C=C}$ bond has a length of 137 pm while the $ce{C=C}$ bonds at the end of the molecule have lengths of 134 pm, the length of a standard $ce{C=C}$ bond. The two carbon-carbon single bonds are 146 pm long, also off from the standard 154 pm length of carbon-carbon single bonds.
Clayden's organic chemistry hints that the explanation has to do with the molecular orbits formed and the conjugation system in the molecule. However, I do not fully understand this explanation.
Why do these carbon-carbon bonds show this unusual bond length behavior? A thourough explanation using MO theory would be appreciated.
References
Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.
organic-chemistry bond molecular-orbital-theory
add a comment |
Hexatriene is an unsaturated hydrocarbon with six carbon atoms and five carbon-carbon bonds, three of which are double bonds.
However, the bond lengths of the $ce{C=C}$ bonds are not the same. The middle $ce{C=C}$ bond has a length of 137 pm while the $ce{C=C}$ bonds at the end of the molecule have lengths of 134 pm, the length of a standard $ce{C=C}$ bond. The two carbon-carbon single bonds are 146 pm long, also off from the standard 154 pm length of carbon-carbon single bonds.
Clayden's organic chemistry hints that the explanation has to do with the molecular orbits formed and the conjugation system in the molecule. However, I do not fully understand this explanation.
Why do these carbon-carbon bonds show this unusual bond length behavior? A thourough explanation using MO theory would be appreciated.
References
Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.
organic-chemistry bond molecular-orbital-theory
add a comment |
Hexatriene is an unsaturated hydrocarbon with six carbon atoms and five carbon-carbon bonds, three of which are double bonds.
However, the bond lengths of the $ce{C=C}$ bonds are not the same. The middle $ce{C=C}$ bond has a length of 137 pm while the $ce{C=C}$ bonds at the end of the molecule have lengths of 134 pm, the length of a standard $ce{C=C}$ bond. The two carbon-carbon single bonds are 146 pm long, also off from the standard 154 pm length of carbon-carbon single bonds.
Clayden's organic chemistry hints that the explanation has to do with the molecular orbits formed and the conjugation system in the molecule. However, I do not fully understand this explanation.
Why do these carbon-carbon bonds show this unusual bond length behavior? A thourough explanation using MO theory would be appreciated.
References
Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.
organic-chemistry bond molecular-orbital-theory
Hexatriene is an unsaturated hydrocarbon with six carbon atoms and five carbon-carbon bonds, three of which are double bonds.
However, the bond lengths of the $ce{C=C}$ bonds are not the same. The middle $ce{C=C}$ bond has a length of 137 pm while the $ce{C=C}$ bonds at the end of the molecule have lengths of 134 pm, the length of a standard $ce{C=C}$ bond. The two carbon-carbon single bonds are 146 pm long, also off from the standard 154 pm length of carbon-carbon single bonds.
Clayden's organic chemistry hints that the explanation has to do with the molecular orbits formed and the conjugation system in the molecule. However, I do not fully understand this explanation.
Why do these carbon-carbon bonds show this unusual bond length behavior? A thourough explanation using MO theory would be appreciated.
References
Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.
organic-chemistry bond molecular-orbital-theory
organic-chemistry bond molecular-orbital-theory
edited 2 hours ago
orthocresol♦
37.9k7111227
37.9k7111227
asked 3 hours ago
Ethiopius
7817
7817
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
If you derive the π-type molecular orbitals of hexatriene, the three lower-energy MOs which are filled would look something like this (image from p 33 of Fleming's Molecular Orbitals and Organic Chemical Reactions, Reference Edition):
I suspect what Clayden is getting at is that in the second MO, there is some antibonding character between C3 and C4, whereas the C1/C2 and C5/C6 interaction is purely bonding.
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "431"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fchemistry.stackexchange.com%2fquestions%2f107102%2fexplanation-for-bond-lengths-in-trans-hexatriene%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
If you derive the π-type molecular orbitals of hexatriene, the three lower-energy MOs which are filled would look something like this (image from p 33 of Fleming's Molecular Orbitals and Organic Chemical Reactions, Reference Edition):
I suspect what Clayden is getting at is that in the second MO, there is some antibonding character between C3 and C4, whereas the C1/C2 and C5/C6 interaction is purely bonding.
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
add a comment |
If you derive the π-type molecular orbitals of hexatriene, the three lower-energy MOs which are filled would look something like this (image from p 33 of Fleming's Molecular Orbitals and Organic Chemical Reactions, Reference Edition):
I suspect what Clayden is getting at is that in the second MO, there is some antibonding character between C3 and C4, whereas the C1/C2 and C5/C6 interaction is purely bonding.
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
add a comment |
If you derive the π-type molecular orbitals of hexatriene, the three lower-energy MOs which are filled would look something like this (image from p 33 of Fleming's Molecular Orbitals and Organic Chemical Reactions, Reference Edition):
I suspect what Clayden is getting at is that in the second MO, there is some antibonding character between C3 and C4, whereas the C1/C2 and C5/C6 interaction is purely bonding.
If you derive the π-type molecular orbitals of hexatriene, the three lower-energy MOs which are filled would look something like this (image from p 33 of Fleming's Molecular Orbitals and Organic Chemical Reactions, Reference Edition):
I suspect what Clayden is getting at is that in the second MO, there is some antibonding character between C3 and C4, whereas the C1/C2 and C5/C6 interaction is purely bonding.
answered 1 hour ago
orthocresol♦
37.9k7111227
37.9k7111227
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
add a comment |
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
And this antibonding interaction between C3 and C4 would cause the double bond to have slight single bond character, which would explain the longer than usual bond length for the C3=C4 bond?
– Ethiopius
1 hour ago
2
2
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
Yes, pretty much. So it is something like a 1.99-bond, if that makes any sense. (That number's made up, of course.)
– orthocresol♦
1 hour ago
add a comment |
Thanks for contributing an answer to Chemistry Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fchemistry.stackexchange.com%2fquestions%2f107102%2fexplanation-for-bond-lengths-in-trans-hexatriene%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown