28.02.2013 Views

Handbook of Solvents - George Wypych - ChemTech - Ventech!

Handbook of Solvents - George Wypych - ChemTech - Ventech!

Handbook of Solvents - George Wypych - ChemTech - Ventech!

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

10.3 Solvent effects based on pure solvent scales 591<br />

( )<br />

S S H H<br />

Δv = v − v = Φ v −32637 −174<br />

[10.3.7]<br />

H<br />

where v S is the absorption wavenumber in solvent S and v H in n-hexane (the reference solvent).<br />

The absorption maxima <strong>of</strong> these ketones depend both on the solvent and on their own<br />

structure.<br />

The Φ values spanned by the 23 solvents studied range from -0.01 for carbon tetrachloride<br />

to 0.65 for formic acid. The values for DMSO and water are 0.115 and 0.545, respectively.<br />

10.3.3.8 The S� scale <strong>of</strong> Drago<br />

Drago 60 developed a “universal polarity scale” (the S� scale) from more than three hundred<br />

spectral data (electronic transitions, 19 F and 15 N chemical shifts and RSE coupling constants)<br />

for 30 solutes in 31 non-protic solvents from cyclohexane to propylene carbonate.<br />

He used the equation<br />

Δχ = SP ′ + W [10.3.8]<br />

where Δχ is the measured physico-chemical property, S� ��� ������� ��������� � ��� ���������<br />

�������������� �� ��� ������ ��� � ��� ����� �� Δχ �� �� � �� ����� �������� �� ��������� �����<br />

���������������������������������������������<br />

The S� scale was constructed from carefully selected data. Thus, it excluded data for<br />

(a) all systems involving any contribution from donor-acceptor specific interactions (donor<br />

molecules where only measured in donor solvents and data for πsolutes were excluded); (b)<br />

concentrated solutions <strong>of</strong> polar molecules in non-polar solvents (which might result in clustering);<br />

and (c) polar solvents occurring as rotamers (each rotamer would be solvated in a<br />

different way).<br />

In order to extend the S� ����� �� ���� ��������� ����� �� ������� �� ���������� �������<br />

��� ���������� ������� ������������ ���� �������� ������������ ����� ��� ������ ������ ������<br />

��� ����� �������� ��� ��������� �� � ���������������� ������� �� ������ ����� ���������<br />

��� ���� �� ����� ��� ������� ���� ��� ������ ��� ��� �������� ������������ ��� �������� �����<br />

������ ��� ���� ��� ����� ����� ��� ������� �� ��� �������������� �� ��� �������� ���������<br />

����� ��� �������� ������� ��� ����� ��� ��� ��������� �� ��� ������� �� ��� ����������<br />

���� ��� ��� ������ ����� ��� ������� �� � �������� �� ��� ������� �������������� �� ��������<br />

������ �� ������ ���������� ��� ������������ ��������� ��������� ��� ��� ������� ��� �����<br />

������ �� ����������� ���������� �� ��� ������� ������ ��������� �� ����� ��� �� ����� ��<br />

��������� 62<br />

10.3.4 SOLVENT POLARITY: THE SPP SCALE 15<br />

As noted earlier, a suitable probe for assessing solvent polarity should meet various requirements<br />

including the following: (a) the modulus <strong>of</strong> its dipole moment should increase markedly<br />

but its orientation remain unaltered in response to electronic excitation: (b) it should<br />

undergo no structural changes by effect <strong>of</strong> electronic excitation or the nature <strong>of</strong> the solvent;<br />

(c) its basicity or acidity should change as little as possible upon electronic excitation so that<br />

any changes will be negligible compared to those caused by polarity; (d) the spectral envelope<br />

<strong>of</strong> the electronic transition band used should not change with the nature <strong>of</strong> the solvent;<br />

and (e) its molecular structure should facilitate the construction <strong>of</strong> a homomorph allowing

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!