5.068  Physical Inorganic Chemistry

Dear class,

I was able to secure a better location for our class, which effective immediately will take place in Building 66, Room 168. Because there is one conflict with our class on the date of 4/29, we will hold class that day in 36-112. I will remind you of that change once we get closer to that date.

On a different note, today's powerpoint slides are now on Stellar. After class, some people seemed confused about the NMR example of the methyl groups exchanging in DMF. In that example, we estimated the approximate exchange rate that the groups need to show in order for their two independent signals to show as an average signal, and we found that based on their difference of about 15Hz, they should exchange at a rate of approximately 100 s-1 in order to coalesce to a single NMR signal. The data shows that at room temperature the two methyl groups indeed start at two distinct sharp peaks, meaning that their exchange rate is lower than that required for signal coalescence. As the temperature increases, each of the independent methyl signals broadens because now the exchange rate increases and the exchange process approaches the relaxation time of the excited state in each case. Smaller (small) delta t, increased (small) delta "frequency". As we increase the temperature even more, the exchange rate increases even more such that the two broadened signals are not distinguished as single signals anymore, but rather as one broad peak (Tc, giving k = 32 s-1). Further increase in temperature leads to further increase in exchange rate and now the average peak simply gets more "average", meaning it gets sharper. At that point the exchange rate may well be 100 s-1.

See you Friday in 66-168!
Mircea

Dear students,

The class time and classroom location previously listed on Stellar were incorrect (however the information accessed through the course catalog and online registration has always been correct).

5.068 will begin on April 1, and lectures are on Wednesdays and Fridays from 10:00am - 11:30am in Building 8, Room 119.

Best wishes,

Lynn Marie Guthrie-Libby & the Chemistry Education Office Staff

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