EXPERIMENTAL DETERMINATION OF STRUCTURE Flashcards
What is the purpose of elemental microanalysis in organic chemistry?
To determine the masses of C, H, O, S, and N in a sample of an organic compound to find its empirical formula.
An empirical formula shows the simplest ratio of the elements in a molecule.
What can elemental microanalysis be determined from?
♦ combustion product masses
♦ percentage product by mass
What does mass spectrometry measure in organic compounds?
Accurate gram formula mass (GFM) and structural features.
What are parent ions in mass spectrometry?
Positively charged molecular ions generated from an organic molecule after electron removal.
What does a mass spectrum plot show?
The relative abundance of the ions detected against the mass-to-charge (m/z) ratio.
How is the molecular formula determined using mass spectrometry?
Using the mass-to-charge ratio of the parent ion and the empirical formula.
Fragmentation data also provides structural information.
What is the role of infrared spectroscopy in organic chemistry?
To identify certain functional groups in an organic compound.
It measures the absorption of infrared radiation by the compound.
What happens to bonds in organic compounds when infrared radiation is absorbed?
They vibrate (stretch and bend).
What units are used to measure absorbance in infrared spectroscopy?
Wavenumbers, the reciprocal of wavelength, in units of cm-1.
This measurement indicates the intensity of transmitted radiation at different wavelengths.
Fill in the blank: Elemental microanalysis shows the _______ of the elements in a molecule.
simplest ratio
What is the relationship between the area under the peak and the number of 1H atoms in that environment?
The area under the peak is related to the number of 1H atoms in that environment and is often given by an integration curve on a spectrum.
How is the height of an integration curve related to 1H atoms?
The height of an integration curve is proportional to the number of 1H atoms in that environment.
What is the standard reference substance used in 1H NMR spectroscopy?
Tetramethylsilane (TMS)
What chemical shift value is assigned to tetramethylsilane (TMS)?
A chemical shift value equal to zero is assigned to tetramethylsilane (TMS).
What are the two types of NMR that can be used to obtain 1H NMR spectra?
Low-resolution NMR and high-resolution NMR.
What is a key difference between low-resolution and high-resolution 1H NMR?
High-resolution 1H NMR uses higher radio frequencies than low-resolution 1H NMR and provides more detailed spectra.
What phenomenon occurs in high-resolution 1H NMR due to interactions with neighboring carbon atoms?
The splitting of peaks into multiplets occurs due to interactions with 1H atoms on neighboring carbon atoms.
What determines the number of peaks within a multiplet in high-resolution 1H NMR?
The number of 1H atoms on neighboring carbon atoms will determine the number of peaks within a multiplet.
What is the n+1 rule in relation to multiplet peaks?
The n+1 rule states that the number of peaks within a multiplet is determined by n, the number of 1H atoms on the neighboring carbon atom.
