ORGANIC ANALYSIS

• What's the difference between an ordinary mass spectrometer and a high resolution (high-res) mass spectrometer?

  An ordinary mass spectrometer are only accurate to the nearest whole number whilst a high resolution mass spectrometer are accurate to several decimal places
• What things do you state when asked to find structure of molecule using IR spec?

  Show your trial and error attempts by stating which bonds can be present by stating which range peaks are and aren't there.
• What range is the fingerprint region in the IR spec and what are you supposed to do with it?

  its range is below 1500 and you don't identify peaks within the fingerprint region.
• How do you distinguish between molecules with the same homologous series/functional group? (2)

  Their fingerprint regions will be unique (1) that can be compared to a database (1)
• What do you do when you can't decide whether there's a peak for C=O or not?

  If there's only 2/3 distinct peaks in the spectrum then a peak in the 1400-1700 range may indicate a peak for C=O (or C=C depending on Q)
• What do you do when you have to decide on whether the molecule is an alcohol, a ketone with a hydroxy group or an alcohol with an alkene group ("en") and there's already a peak for an O-H bond and there's a peak in the 1600-1800 region?

  You have to eliminate the alcohol without a carbonyl group/carbon-carbon double bond because there is a peak in the range where either a C=C or C=O lies.

  Then see whether the peak lies closer to the 1620-1680 range (likely to be the alcohol with the alkene group) or nearer the 1700's (because then it's likely to be the ketone with a hydroxy group)
• What shape peak is an O-H ALCOHOL bond likely to have in the IR spec?

  A whale's head shape
• What shape is a an O-H ACID bond likely to have in the IR spec?

  A Mountain shape
• What can you tell about the compound if there's only a peak for 1 functional group in the IR spec?

  That there's 2 of that functional group in the compound (e.g if there's a whale head shape on the IR spec and no other peak above fingerprint region then there's 2 alcohol groups within the compound)
• What are the 3 types of chromatography techniques?

  Thin layer chromatography (TLC)

  Column chromatography

  Gas chromatography
• How does TLC (thin layer chromatography) work and what's the stationary and mobile phase?

  first coat a thin layer of glass, plastic or metal with a thin layer of silica or alumina gel

  then spot a small drop of the sample on a pencil line near the bottom of the plate and dip it into a solvent

  The mobile phase is the solvent and the stationary phase is the alumina/silica gel
• What are the factors that affect the rate of movement up the TLC plate?

  Retention by the stationary phase (higher retention can slow movement up the plate and there's higher retention when when the molecule is polar or the molecule forms hydrogen bonds with the stationary phase)

  solubility of the molecule in the moving phase (if solubility is high the particle moves further up the plate, there's increased solubility in the moving phase when the molecule and the moving phase are both non-polar)
• What do use to record the results of the TLC and what equation is used?

  Rf values used and to calculate Rf you divide distance travelled by the component by the distance travelled by the solvent.
• To how many decimal places do you give Rf values?

  To 2d.p
• When is a molecule's Rf value closer to zero and when is it closer to 1?

  Closer to zero: When the molecule moves a short distance on the chromatography plate (molecule has greater retention to the stationary phase).

  Closer to 1: When the molecule moves a long distance on the chromatography plate(when the molecule has a higher solubility in the moving phase) .
• When does a molecule have a higher retention to the stationary phase and when does a molecule have a higher solubility in the moving phase?

  The molecule will have higher retention to stationary phase if both the molecule and the stationary phase/TLC plate are polar

  The molecule will have a higher solubility in the moving phase if the solvent/moving phase and the molecule are non-polar
• What do you do if a component is colourless and you need to work out its Rf value on a TLC?

  Either spray a developing agent on the chromatogram to make it show up or add a substance which fluoresces under UV light to the stationary phase such as ninhydrin
• How does column chromatography work?

  The stationary phase is packed into the column

  the sample is then added on top of the stationary phase

  The moving phase/eluent on top of the sample then washes down the different components which elute separately
• How does gas chromatography work?

  the moving phase is a gas

  the stationary phase is a powder or a powder coated with a viscous liquid (oil)

  sample then passes through long thin tube which is heated to a specific temperature

  The detector identifies when each of the components reaches the end of the tube
• How is the gas chromatography data displayed?

  In a graph with different peaks for different components where the height of the peaks represents how much of the component eluted (came out of the tube) at each moment.

  The area of the peak represent the component's abundance

  The position of the peak on the x-axis represents time spent by the component in the tube (this is the retention time)
• Why is retention time important for both gas and column chromatography?

  Because it gives an indication of the polarity of the components (e.g if the stationary phase for gas chromatography is non-polar then the non-polar component will have a higher retention time than the polar component)
• what's necessary for carbons to be in the same environment (for C-13 NMR) ?

  They have to have the same set of neighbouring atoms the same number of bonds away from each other
• What's a symmetry based shortcut that'll allow you identify carbons in the same environment (for C-13 NMR) ?

  when you can reflect a molecule so that the molecule looks identical after reflecting it, the carbons that swap positions after the reflection will have the same carbon environments. (e.g if there's propanone the carbons on either side of the C=O bond have the same environments)
• In a C-13 NMR what does the number of peaks represent?

  The number of peaks is equal to the number of carbon environments in the compound that produced the NMR spec
• In a C-13 NMR what does the position of the peak represent?

  The position of the peak gives information about what atoms are bonded to the carbons in that environment because the position of the peak is basically the ppm value from the data booklet.
• What is the standard used in the C-13 spec and why is it used?

  Tetramethylsilane (TMS) because it only has 1 carbon environment,

  the TMS peak doesn't interfere with the sample peaks

  it has a low boiling point so it can be easily removed.

  It's peak is at a low chemical shift
• If you're asked to deduce the structure of a compound given the number of peaks in its C-13 NMR spec and the molecular formula of the compound what's a tactic you can use?

  Check if the number of peaks in its spec are the same as the number of carbons in the compound, if it is then there's no symmetry within the carbon chain of the compound.

  If the number of peaks in its spec are lower than the number of carbons in the compound, then the compound's carbon chain has some symmetry
• How do you find the structure of a molecule given its molecular formula and its C-13 NMR spec?

  First identify how many different carbon environments there are by counting the number of peaks in the spec

  Look at the ppm values for each peak to identify what exactly each carbon is bonded to

  then suggest a structure by doing these two things
• What's the standard for the hydrogen NMR and what's required in the solvent of a Hydrogen NMR ?

  TMS (tetramethylsilane) is the standard and there should be no Hydrogen in the solvent or you can have just isotope deuterium
• What does the area of a peak/the integration value in a proton NMR indicate?

  It tells you the number of Hydrogen atoms in each enviroment
• What does the splitting pattern of a H1-NMR spec indicate about the compound?

  The type of splitting pattern indicates how many hydrogens there are on the atoms adjacent.

  If there's a triplet peak then there are 2 hydrogens on the atom adjacent

  If there's a quartet peak then there are 3 hydrogens on the atom adjacent

  If there's a doublet peak then there's 1 Hydrogen on the atom adjacent

  If there's a singlet peak, there's no hydrogens on the atom adjacent
• What are the exclusions to the "n+1" splitting rule and what does the peak look like instead?

  a Hydrogen bonded to an oxygen or nitrogen doesn't split instead it's a broad singlet.
• What does the number of peaks in the proton NMR indicate?

  How many hydrogen environments there are
• What does it mean if a peak in the proton NMR is larger than the others?

  it means that this peak has the highest integration value (most number of hydrogens in its environment)
• What does the height of the peak in the C-13 NMR indicate?

  It indicates the number of carbons in that environment.
• What splitting pattern will a O-H bond with integration value of 1 have (in the proton NMR spec) and why?

  It will have a singlet splitting pattern (so no hydrogens adjacent) because the O from O-H interferes with anything else bonded next to it/interferes with any other hydrogen environments so that those other hydrogen environments don't count and the splitting pattern will always be a singlet.
• How do you structure your marking points for the proton NMR structure analysis?

  State what splitting pattern there is and at which ppm it's at, then state what the integration value is and then state what the splitting pattern tells you about what's adjacent. (e.g if quartet, it's next to a CH3)
• What can you do to help you deduce the structure of a compound after you've identified all the bonds there can be from the peaks?

  draw out all the bonds in a displayed format (especially for the proton nmr to help you visualise what bonds are next to each other) and use the molecular formula to count and check if you've got the right numbers of molecules.
• what does the splitting pattern on a H+ NMR indicate?

  the peak will split into the number of H's on adjacent environment + 1 so if it's a triplet then there are 2 H's on adjacent environment
• what does a quartet peak and a triplet peak in an NMR spec suggest?

  that there's a CH3CH2 group