N-14 NMR

How can 14^N be NMR active if it has 7 N and 7 Protons? I understood the text as both must be even numbers for the nucleus to be active (TA). (Not quite. If the number of neutrons and protons is odd, the nucleus is always magnetic, because the magnetic moments of individual nuclei can not compensate for each other. If this number is even, they usually do, and the nucleus is not magnetic. Sometimes, the magnetic moments of nuclei are aligned (two nuclei have the same magnetic moments, instead of the opposite moments), and then the nucleus is magnetic. 14N is an example (so-called quadrupole nucleus). Another simpler example is deuterium (2H) - GS. 

I was reviewing through the lecture slides and came across the following question: Why do we not consider absorption of IR by N2 and O2, which are way more abundant in the atmosphere, then CO2? Is the answer because N2 and O2 are symmetrical, unlike CO2, and therefore they have a negligible dipole moment; and, with IR absorption such as in IR spectroscopy, a dipole moment must be present in order for IR to be absorbed? Thank you. (Almost. We need to consider change of the dipole moment, not the dipole moment itself. - GS).

Why is carbon 13 used instead of carbon 12 for NMR? (Because Carbon 13 is magnetic, and carbon - 12 is not. - GS).

How does a chiral center affect the number of signals in H-NMR? (It can make some nuclei diastereotopic, and therefore, non-equivalent, so the number of signals increases. - GS).

What makes a peak more intense in IR Spec? (Larger change in the dipole moment during the vibration, corresponding to that peak. - GS).

Would you be able to explain NMR coupling strength between axial and equatorial hydrogens once more? How do you know which hydrogens will couple? (Axial H with an axial H at the adjacent carbon will couple the strongest, because the dihedral angle is 180o. Axial and equatorial hydrogens or equatorial and equatorial hydrogens also couple, but much weaker, because of the less favorable dihedral angle. - GS).   Thanks.

Does electronegative atoms cause shielding or deshielding of the atoms near it? (Deshielding, because shielding is caused by electrons. - GS). If there is deshielding then it is upfield and there is less of a chemical shift and if there’s shielding it’s more downfield and has more of a chemical shift correct? Am I backwards on this or do I have it correct? Thanks. (It is backwards, because shielding requires more field to overcome the shielding, so it is upfield. - GS).

If something is a triplet there are two coupling partners correct? (Yes, but the partners must be equivalent. - GS).

What exactly is coupling? I am confused with the H atoms and their spin. (It is dependence of the resonance frequency of a nucleus on the spin state of other nuclei (=its coupling partners) - GS).

What is the difference between electric and magnetic waves? Does one have higher wave frequencies than the other? (A change of the electric field causes a change of the magnetic field, and vice versa, so both components have same frequency. - GS).

I understand the vibration between certain bonds but if one has electric does it vibrate at high frequencies or not? I’m having a hard time grasping the broad idea of it.  (The IR absorption takes place only if it causes a change in the dipole moment of the molecule. - GS).

What’s the difference between an epimer and a diastereomer? I have written in my notes that configuration of only one center is opposite for both of them. Thanks. (Epimers are different by the configuration of one chiral center. They can be diastereomers. - GS).

What are the main differences between an H-NMR spectra and a C-NMR spectra?  (1. The resonating nucleus. 2. Its natural abundance. 3. Use of decoupling techniques. - GS).

Can you talk about the Coupling Constant again and its significance? I’m not understanding it. The coupling constant shows by how much the resonance frequency of a nucleus is affected by the spin state of another nucleus. - GS).

How do you know which C=C bond in two different molecules will produce a stronger signal? Would you go over this in class? (It depends on the dipole moment change. - GS).

Can you explain homotrophic and enantiotrophic molecules in class? (Here is a good resource: http://www.masterorganicchemistry.com/2012/04/17/homotopic-enantiotopic-diastereotopic/  - GS).

How do you know if a signal is upfield or downfield? (Chemical shift increases from upfield to downfield. - GS).

How many different kinds of protons are in 1-chlorohexane? I found the answer to be 6 but I can only find 5 different types of protons. (Each of 6 carbons is bonded to a different type of protons, so the answer is 6. - GS).

^Can you explain how the protons connected to the 3 and 4 carbons of 1-chlorohexane are different? (Substitution of a proton of the first type with chlorine would give 1,3-dichlorohexane, while the substitution of the second one - 1,4-dichlorohexane. Substitution of chemically equivalent protons leads to the same compound. - GS).

How do we tell the difference between an alkyne and an alcohol on an IR spectrum?  (Stretch of the triple bond. - GS).

On the Wiley homework there is a section about whether or not to expect an IR signal above or below 3000 cm^-1. For a few of the alkenes and alkynes it says that we should not expect a signal above 3000, but today in class we were told to expect C-H stretching above 3000 cm^-1. Can you clarify that? (This stretching is characteristic for H connected to an sp2- or sp-hybridized carbon, which is a part of a C=C bond or carbon-carbon triple bond. Therefore, this vibration will be observed for alkenes and alkynes with at least one H at a multiple bond, and will not observed for the rest of them. - GS).

If a molecule has a temporary dipole moment, is it infrared-inactive or infrared-active? (A molecule is infrared-inactive if the vibration does not change the dipole moment. All molecules undergo polarization and have very short-lived dipole moments. I have not heard that it affects their IR-behavior. But never say never, some ultrafast instrumentation might detect those fluctuations if they occur slower than IR-induced vibrations. - GS).