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If I take a compound like cyclopentadiene ($\ce{C5H6}$) and I substitute a nitrogen for a carbon at one of the $\ce{C=C}$ bonds (making a $\ce{C=N}$ bond), how does this typically change the hydrophobicity of the compound?

The problem is that I'm not really a chemist. My thought here is that nitrogen is more electronegative than carbon, so this will polarize the bond, induce a dipole, and make the molecule more hydrophilic. In general, it seems to me that mixing together atoms of differing electronegativity in alkane or alkene/etc. compounds should create dipoles that can interact with polar solvent molecules, improving hydrophilicity.

As an additional thought, how would the nitrogen substitution effect stacking interactions between the substituted ring and a regular molecule of cyclopentadiene? My guess here would be that hydrophobic effects would cause a more favorable pi-stacking interaction between two unsubstituted copies of cyclopentadiene relative to cyclopentadiene and the aforementioned and described nitrogen substituted version of the molecule.

To clarify, by "stacking interactions" I mean the sort of $\ce{C=C}$ stacking interactions that lead to cycloaddition reactions, not that the two rings will lie on top of one-another (as in the case of something like a pair of benzene molecules).

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The cyclic unsaturated imine (Schiff base) will be more hydrophilic for the nitrogen lone pair hydrogen bonding and being a Lewis base toward water. You do know that CpH [4 + 2} Diels-Alder reaction reversibly thermally dimerizes, right? The endo-dimer is an exo-flip then hydrogenation away from JP-10 cruise missile fuel.

The cyclic imine, ${2H}$-pyrrole is an isomer of pyrrole. One expects it will be labile toward proton migration in base.

http://www.chemspider.com/Chemical-Structure.7330.html
http://www.chemspider.com/Chemical-Structure.5256848.html
Click the Properties tab, etc.

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  • $\begingroup$ Thanks, didn't know about the jet fuel composition. :) Do you know if the lone pair will effect stacking? $\endgroup$ – user5420 May 6 '14 at 1:32
  • $\begingroup$ Neither the imine nor CpH is aromatic for the ring methylene. There will be adverse steric interactions if two such molecules approach. $\endgroup$ – Uncle Al May 6 '14 at 3:29
  • $\begingroup$ I thought one could perhaps have offset stacking interactions between the two CpH rings? Where just a pair of double bonds stack on one-another? $\endgroup$ – user5420 May 6 '14 at 10:23
  • $\begingroup$ As you say, there is a CpH / CpH cycloaddition reaction, so I thought this requires this sort of edge-wise stacking interaction? $\endgroup$ – user5420 May 6 '14 at 10:42
  • $\begingroup$ @user5420 In the transition state of the Diels-Alder reaction, the 2 CpH molecules are stacked with their double bonds perpendicular to each other, as it is, for example, shown in the image on orgo.curvedarrow.com/punbb/viewtopic.php?id=144. $\endgroup$ – Jannis Andreska May 6 '14 at 12:39

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