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Advanced Inorganic
Topics Class-Dr. Brian Barry
| Question | Answer |
|---|---|
| if you think you synthesized "something" new or interesting or know a compound, how do you convince someone else that you know what you made? | look in literature; use an array of necessary/appropriate analysis methods to make your case |
| chemical analysis is key for quantitative information on | atomic compositions and chemical reactivity |
| chemical analysis of metals | atomic absorption/emission spectroscopy (AA/AE) |
| chemical analysis of gases/organic compounds | oxygen-based combustion analysis (CHN converted to CO2, H2O, N2 gases) |
| chemical analysis of ions | classical ion-selective detection (ex. flame tests) |
| most chemical analysis methods require the destruction of the chemical uniqueness and atomic connectivity of your | inorganic/organic materials (aka sample) |
| what types of "physical" analyses are applicable to inorganic chemistry? | that depends strongly on what type of inorganic structure/material you are studying |
| which is easier to study molecules or extended materials | molecules because they are easier to dissolve |
| when the nuclear spin quantum number (I) value = 0 | the nuclei is unaffected by a magnetic field (ex. 12C) |
| as the atom size increases the Larmor frequency | decreases because it takes longer to turn over |
| T1 is the relaxation time also described as | the time required for the nuclei to come back up after being knocked down; different rate for each nuclei |
| 1 T is how many MHz | 42.6 MHz |
| a magnetic field of 1T induces a Larmor frequency of how much in a proton | 42.6 MHz |
| for a given nucleus with a nuclear spin, I there are how many degenerate states possible | 2I +1 |
| NMR is a super conductor containing electrons rotating | counterclockwise |
| in NMR a constant magnetic field is generated from electricity, the stronger the field is it easier or harder to flip an electron | harder |
| free induction decay | wavelength released from a charged electron as it flips back to it's relaxed mode |
| Fourier transforms changes the RF signal (intensity vs. time) to | x-axis of ppm |
| how does ppm relate to frequency | range is roughly 15-0 ppm for 1H NMR but different standards can be chosen (scaling factor) |
| absorption of energy by nucleus with a nuclear magnetic moment is called | resonance (spin changes relative to applied magnetic field). The change in energy is dependent on magnetic field strength |
| a brief (microsecond) RF pulse causes transitions from ground nuclear spin state to | excited nuclear spin state transition (M (I)= +1/2, -1/2) |
| sensitive RF detector coil records the | time spectrum that is converted to frequency domain by FT |
| most modern magnets are not perfectly stable, so they need to maintain a lock on a specific nucleus and then adjust the | field slightly to keep the resonance energy of this nucleus unchanged |
| since energy increases as the magnetic field increases recording absorption processes on different instruments | will lead to different frequency values |
| since only ppm differences exist with different resonance frequencies, it is crucial that all nuclei see the same external magnetic field; how do we make it homogeneous | a. spin a dissolved solution sample very fast (~20 Hz) b. fine tune imperfections in applied magnetic field and glass tube by electronic shimming |
| why do peaks appear at different relative resonance energies/frequencies? | define Heff=net magnetic field implying on the nucleus of interest |
| chemical shift is dimensionless but is generally reported in ppm to | make it the same on different NMR |
| EPR | sample is held in a very strong magnetic field while electromagnetic radiation is applied monochromatically |
| Magnetic susceptibility | is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field (k) |
| diamagnetism | materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are repelled by the applied magnetic field. |
| paramagnetism | a form of magnetism whereby certain materials are attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. |
| ferromagnetism | the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets |
| units for u (mu) | magnetic moment; A(m^2) or J (T^-1) |
| CHNS beings by wrapping a sample in | aluminum foil |
| CHNS sample is dropped into a chamber with | 5% He (carrier gas) and 95% O2 (combustion) and the sample hits a heated filament |
| CHNS the sample is combusted and the volitle components are carried away by | He |
| In CHNS we need to decrease oxygen to the point that it is | out of the gas stream and we do this with high surface area copper catalyst |
| how to we get rid of the oxygen in CHNS | high surface area copper catalyst; CuO forms on surface and you are left with He, CO2, H2O, N2, and SO2 which enter the GC |
| what components of CHNS enter the GC | He, CO2, H2O, N2, and SO2 |
| using standards in GC we can relate peak intensity to the | concentration/mass of the sample |
| what are somethings that can go wrong in CHNS? | not all of it combusts; metal carbides form |
| if carbides form in CHNS the GC readout will have a low levels of | carbon because not all of it reacts |
| how do you counteract the formation of carbides in CHNS | add WO3 and/or Ta2O5 catalysts which catalyze the combustion (make the reaction happen so fast that the metal carbides can't form) |
| what does CHNS detect? | carbon, hydrogen, nitrogen, and sulfur |
| solid state chemistry deals with | extended materials held together by ionic or covalent bonds |
| in extended materials where are the electrons | shared over the whole material; not localized |
| extended materials have a higher boiling point and a lower volatility than | molecules |
| solid-state chemistry is the study of | well-ordered crystals, often flawless on near (mm) length scale; syntheses target new compositions with often complex structures and new physical properties |
| materials chemistry is the | synthesis & study of extended solids (ex. highly disordered structures, low dimensional polymers, solids with nanoscale dimensions); often manipulate known solids to achieve new & useful physical or chemical properties |
| 4 general characteristics of molecules and molecular solids | discrete units (usually under 10 covalently bonded atoms), valence e-s localized bonds or MOs, synthesis often at low temperatures, may be soluble |
| 3 general characteristics of solid-state structure | large number of interconnected atoms or ions held together by covalent and/or ionic forces, bonding by valence e-s in orbitals that are dispersed in bands, synthesis at high temps |
| the ceramic method is also known as | "heat and beat" or "shake and bake"; mix and heat to react; directly react the components at high temperatures |
| Thin film growth | chemical vapor deposition (CVD); A(g) + B(g) = C(s)film + byproduct gases |
| solution nanoparticle growth (<100 nm particle sizes) | particle growth (nucleation and precipitation) from eated solution of reactive precursors-AB compounds may require a subsequent high-temperature annealing (or use very hot solutions) step to complete reaction and form crystalline product |
| we need a reaction vessel that removes air/O2 from reaction how do we solve this | load both reagents into a sealed, evacuated glass ampoule |
| remember PV= | nRT calculation for gaseous reagents, intermediates, and byproducts |
| stable solid reagents (e.g. Ti Metal) require substantial external energy to react; so we need to heat the elements in a furnace and the thermal limits of the | reactor need to be considered |
| ampoules for heating air-sensitive reactions are made from | pyrex (use up to ~550 degrees C in a vacuum); silica (pure SiO2 up to ~1200 degrees C) |
| SiO2 will not crack upon rapid cooling (drop in water) but Pyrex | will (thermally expansion coefficient is large) |
| what are the experimentally determined "best" reaction conditions for TI and S8 | mix powders in a sealed evacuated Pyrex ampoule; heat at 400 degrees C, intermittently cool, remove partially reacted powder, grind it to expose reactive Ti surfaces, and reheat in an ampoule; heat in a silica vessel at high Ts for a week |
| problems with glass ampoules | reagent attack on glass walls; ampoule explosions due to gas pressure release |
| how do you solve reagents sticking to the glass ampoules walls | add a second protective liner to the sealed glass ampoule (dual containment) |
| how do you solve an ampoule explosion due to gas pressure release | use a glass tube with flowing inert gas |
| resistively heated components (controlled current/voltage through metal wire) | heating tape or mantles; lab tube or box furnaces; furnaces with special heating elements; resistive heating (inert conditions) of graphite or a metal foil |
| exotic heating methods | induction heating; electric arc/discharge; high wattage halogen bulb or infrared bulb heaters |
| grinding helps maximize the | surface area of compounds |
| two solids can "diffuse" into each other but they would take | an incredibly long time to do this by themselves |
| NMR is a resonance technique involving absorption of what type of frequency energy | radio frequency energy |
| the magnetic environment of a nucleus affects its resonance frequency and allows what type of information to be deduced (hint NMR) | structural information |
| to be NMR active the nuclei must poses a nuclear spin (nuclear angular momentum) (I) that does not equal | 0 |
| In the absence of an applied magnetic field, the different nuclear spin states of a nucleus are | degenerate |
| Are the nuclear spin states of a nucleus degenerate in the presence of an applied magnetic field? | no |
| With nearly 100% abundance the 1H NMR spectrum is contributed by how many hydrogen atoms in the sample | virtually every one |
| Which nuclei are suitable for NMR spectroscopic studies? | ones with an I value that doesn't equal 0; helpful if it exists in high abundance; helpful if the T1 (relaxation time) is relatively short |
| possession of a quadrupole moment leads to short values of T1 but tend to cause the peak to | broaden |
| a particular nucleus absorbs characteristic radiofrequencies (it resonances at the frequency). If an NMR spectrometer is tuned to a particular resonance frequency | only a selected NMR active nucleus is observed |
| ex. only 1H nuclei are observed if a 400 MHz spectrometer is tuned to 400 MHz, but if the same spectrometer is returned to 162 MHz, only | 31P nuclei are observed (just like tuning a radio and receiving one station at a time) |
| Nonequivalent nuclei of the same element resonate at different frequencies and therefore have different | chemical shifts |
| although chemical shift does not technically have units it is recorded in ppm so as to show that | the value was multiplied by 10^6; it was multiplied because the values were so small |
| different reference compounds can be used to place 0 ppm; one example is | TMS; CD3Cl |
| the closer a ppm value is to 0, is the frequency higher or lower | lower |
| deuterated solves are used so that | the 1H NMR spectra are not swamped with unnecessary hydrogen signals |
| integration of a peak is proportional to | the number of nuclei giving rise to the signal (ex. 1:3) |
| Coupling results from one hydrogen's magnetic field being associated with | another hydrogen's magnetic field |
| coupling constant J is measured in Hz and describes | the distance between two coupled peaks |
| proton-decoupled is represented as {1H}, what are decoupled experiments | NMR experiments where certain nuclei are "hidden" on the radiofrequency |
| What is the Larmor frequency of a 31P in 3T magnetic field? (note in 100 MHz NMR 31P=40.5 MHz) | 51.8 MHz |
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