Question

1. Why was 7% by weight boric oxide used to make the silly putty? Why would 5% give a tacky material and 10% too dry a product? Discuss full
2. (ii) Draw ALL of the possible isomers of Cl2Sn(O2C5H7)2. How does 1H NMR and IR spectrometry help to distinguish one geometrical isomer from another? Discuss fully.

Add B2O into crude silicon oil after 1.5～2hours

only question 2 need to be answered

Answer 1

There are total three isomers of this compound which are drawn below

(trans) له) (من) - ه - (4) رهن )

(C₅H₇O₂ is acetylacetonate ligand)

Here, cis and trans are geometrical isomers. Cis form is optically active because it has no plane of symmetry and center of symmetry. So these cis (d) and (l) are optical isomers that is, one is dextrorotatory and other is laevorotatory.

1 H NMR to distinguish geometrical isomers.

Geometrical isomers can be distinguished using coupling constant (J) value, which measures the distance between split peaks in Hertz. For cis isomers the value of J is between 10 to12 Hz, while for trans isomers the value of J is between 6 to 8 Hz.

IR to distinguish geometrical isomers.

Geometrical isomers can be distinguished using IR on the basis of change in dipole moment during absorption. Change in dipole moment is more in cis isomers than trans isomers because trans isomer is highly symmetrical and trans isomer has no net change in their dipole moment. The C=C stretching in trans is not observed in IR spectrum, while C=C stretching is observed in cis isomers in IR spectrum.