Spectroscopy

Question 1

What is a mass spectrometer used for?

Answer 1

examines ions derived from molecules (molecular mass)

can’t be used to tell apart isomers

Question 2

What does UV-VIS spectroscopy show?

Answer 2

if any double bonds are present by raising π electrons from lower energy bonding molecular orbitals to higher energy anti bonding molecular orbitals.

Question 3

All molecules containing a non conjugated C=C show an absorption at

Answer 3

170nm due to a π to π* electron transition

Question 4

All molecules containing a non conjugated C=O show an absorption at

Answer 4

250nm due to an n to π* electron transition

Question 5

What is a molecule with conjugated bonds mean?

Answer 5

this with alternating single and double bonds

Question 6

Is electron excitement smaller or larger with conjugated molecules

Answer 6

smaller, thus the absorption is observed at longer wavelengths

Question 7

State Beer’s law

Answer 7

A = Ebc (abdosrbancy has no units)

Question 8

What does IR spectroscopy tell us about bonds?

Answer 8

Bond bending and stretching

Question 9

What are the two ways bonds can stretch

Answer 9

asymmetrically and symmetrically

Question 10

What are the three ways bonds can bend?

Answer 10

in plane scissoring
in plane rocking
out of plane twisting

Question 11

In an IR spectra will asymmetrical bonds show absorption?

Answer 11

Yes they will.

Symmetrical bonds show no IR absorption

Question 12

IR, UV-VIS and MS give no information on

Answer 12

hydrocarbon skeleton, but NMR can

Question 13

in the C13 NMR spectra sp3 carbons show signals between

Answer 13

0-90

Question 14

in the C13 NMR spectra sp2 carbons show signals between

Answer 14

100-210

Question 15

Why is it that sometimes more than one carbon only produces one signal?

Answer 15

carbons in identical environment that are symmetrical only produce one signal