Chemistry and Biochemistry at Low Temperatures 



177 



the new band anticipated in the ultraviolet does not appear within a day or 

 two. Figure 6 indicates what happens when such a solution is warmed. At 

 146°K the absorption band shown is due to the iodine-propene molecular 

 addition compound which has been identified in a previous experiment. At 

 150°K appears the anticipated new band arising from the compound iodine- 

 isoprene. At 154°K, this band quickly disappears irreversibly and at the same 

 time decoloration of the solution occurs. The molecular iodine has been removed, 

 presumably by the halogenation of the double-bond system of isoprene, just 



0. 



q: 

 o 



(J) 



CD 



WAVELENGTH 



Fig. 6. Isoprene dissolved in 1 : 1 propane-propene to which iodine dissolved in 

 1 : 1 propane-propene has been added. The new absorption band which appears 

 at 1 50°K is due to a 1 : 1 molecule addition compound of the iodine to isoprene. 

 Its disappearance at 154°K is due to an irreversible reaction, probably 

 halogenation across the double bond. 



as had occurred when solid iodine reacted with isoprene at the temperature 

 of dry ice. This oxidation appears to require the prior formation of the inter- 

 mediate molecular addition compound stable at about 150°K at the concen- 

 trations employed. 



By investigating the properties and reactions from the lowest practicable 

 temperature upward we would observe the appearance of new thermally 

 activated states and their subsequent reactions. 



