3. Spectroscopy Flashcards
What is the Beer-Lambert law?
this relates to the absorbance (A) of a solution to the molar absorbance coefficient (ξ) of the absorbing species, the concentration © of the absorbing species and the path length of the cell (l), via the equation A = ξ c L
What is bending?
a type of vibration that changes bond angles
What is Chemical shift (δ)?
the quantity used in NMR spectroscopy to identify the positions of signals produced by the nuclei of a sample. The unit of chemical shift (δ) is parts per million (ppm)
What is 13C-NMR spectroscopy?
Nuclear magnetic resonance spectroscopy of carbon atoms within molecules. It provides information about the carbon-hydrogen framework of a molecule
What is a complex splitting pattern?
a splitting pattern resulting from more than one set of equivalent hydrogen atoms. Signals of this type are called multiplets
What is a correlation table?
a table of data on spectroscopic absorption patterns of selected functional groups
What does deshielded mean?
describes the situation in NMR spectroscopy in which resonance or inductive effects reduce the electron density around a nucleus, thus increasing the ability of an applied magnetic field to bring the nucleus into resonance
What is a doublet?
a signal in 1H-NMR spectroscopy that has been split into two peaks in a ratio of 1:1
What does downfield mean?
Describe a signal in NMR spectroscopy that is towards the left of the spectrum or of another signal
What is electromagnetic radiation?
energy propagated through space in the form of oscillating electric and magnetic fields
What is electron spin resonance (ESR)?
a methods of locating electrons within the molecules of a paramagnetic substance
What are equivalent hydrogen atoms?
hydrogen atoms that are chemically equivalent
What is the fingerprint region?
in infrared spectroscopy, the region of the spectrum from 1000 to 400 cm-1
What is frequency?
the number of full cycles of a wave that pass a given point in a second
What is Hertz (Hz)?
the SI unit of frequency. One hertz equals one wave cycle per second
What is high resonance mass specroscopy?
a technique that allows the precise measurement of the mas to charge ratio of ions
What is 1H-NMR spectroscopy?
nuclear magnetic resonance spectroscopy of hydrogen atoms within molecules. It provides information about the carbon-hydrogen framework of a molecule
What is the index of hydrogen deficiency?
the sum of the number of rings and π-bonds in a molecule
What does infrared active mean?
any vibration that results in the absorption of infrared radiation. For a molecule to absorb infrared radiation, the bond undergoing vibration must be polar and its vibration must cause a periodic change in the bond dipole; the greater the polarity of the bond, the more intense the absorption
What is infrared radiation?
the portion of the electromagnetic spectrum with wavelengths in the range 7.8 x 10-7 m to 2.0 x 10-3m
What is integration?
a mathematical process used for determining the area under a signal in an NMR spectrum
What are lines of integration?
a curved line at a signal on a 1H-NMR spectrum that allows the determination of the relative number of hydrogen atoms giving rise to that signal
What is a local magnetic field?
the magnetic field generated by electrons surrounding a nucleus
What is mass spectroscopy?
a technique used to determine the mass of molecules and fragments of molecules
What is a molecular ion?
an ionised molecule that produces a peak in a mass spectrum. This is usually the peak with the highest m/z value
What is a mulitplet?
the splitting pattern of a complex signal in 1H-NMR spectroscopy
What is multiplicity?
the splitting pattern of a signal in 1H-NMR spectroscopy, which can be described as, singlet, doublet, triplet, quartet, multiplet etc.
What is the (n + 1) rule?
a rule for determining the splitting patterns in NMR spectroscopy. If hydrogen atom has n other hydrogen atoms that are not equivalent to it, but are equivalent to each other, on the same or adjacent atom(s), its 1H-NMR signal is split into (n+1) peaks
What is nuclear magnetic resonance (NMR) spectroscopy?
a spectroscopic technique that measures the absorption of energy by nuclei in the presence of a magnetic field
What is a quartet?
a signal in 1H-NMR spectroscopy that has been split into four peaks in a ratio of 1:3:3:1
What is a radical cation?
a species with a positive charge and an unpaired electron
What is radio-frequency radiation?
the portion of the electromagnetic spectrum with wavelengths greater than a metre
What is a reference compound?
a compound added to a sample to be studied by NMR spectroscopy, usually TMS. The positions of the signals in the spectrum are then compared with those of the reference compound
What is resonance?
the absorption of electromagnetic radiation by a spinning nucleus and the resulting flip of its nuclear spin state
What does shielded mean?
describes the situation in NMR spectroscopy in which local magnetic fields from electron surrounding a nucleus decrease the ability of an applied magnetic field to bring the nucleus into resonance
What is signal splitting?
a phenomenon in NMR spectroscopy in which the 1H-NMR signal from one set of hydrogen atoms is split by the influence of neighbouring non-equivalent hydrogen atoms
What is a singlet?
a signal in 1H-NMR that has not been split
What is a splitting pattern?
the pattern obtained when a signal in a 1H-NMR spectrum is split by the influence of neighbouring non-equivalent hydrogen atoms. These can be described as multiplets, singlets, doublets, triplets, quartets etc.
What is stretching?
a type of vibration that changes bond lengths
What is tetramethylsilane (TMS)?
the reference standard used in NMR spectroscopy. Its signal is set at δ = 0
What is a triplet?
a signal in 1H-NMR spectroscopy that has been split into three peaks in a ratio of 1:2:1
What does upfield mean?
describes a signal in NMR spectroscopy that is towards the right of the spectrum or of another signal
What is UV/visible spectroscopy?
a technique used to study compounds that absorb light in the ultraviolet-visible region
What is vibrational infrared?
the portion of the infrared region with a frequency range of 400-4000cm-1
What is wavelength (λ)?
the distance between any two consecutive identical points on a wave
What is wavenumber?
the number of wavelengths per centimetre. The unit of wavenumber is the reciprocal centre metre (cm-1) and is commonly used infrared spectroscopy
What is X-ray crystallography?
the study of crystal structures by X-ray diffraction techniques
What spectroscopic technique is used to determine molecular weight of a compound?
Mass spectroscopy
How many decimal places does High-resolution mass spectroscopy give an accurate reading to?
Five decimal placed
What spectroscopic technique is used to detect functional groups?
Infrared (IR) spectroscopy
What determines whether a bond is detectable via IR spectroscopy?
It must have a dipole moment
What is the most useful spectroscopic technique?
Nuclear Magnetic Resonance (NMR) Spectroscopy
What does NMR detect?
Functional groups
Number of different groups
Connectivity of different groups
How do you determine the number of hydrogens in a particular environment?
The area under the peak of the NMR graph
What is the units used in NMR?
Parts per million (not a concentration)
What is the chemical shift of Tetramethylsilane (TMS)?
0
True or false: If a molecule has a plane of symmetry it simplifies the NMR spectrum and we only need to examine one half to determine the NMR spectrum
True
Do chemically equivalent protons show splitting?
No
Why does splitting occur in NMR?
The protons can be influenced by the magnetic fields of the neighbouring hydrogens.
What is the formula for determining the number of protons per hydrogen environment based on NMR data?
n + 1 peaks (n = equivalent hydrogens)
Where would a band be seen for an alcohol undergoing IR spec?
Broad peak around 3000-3500cm-1
Where would a band be seen for a molecule with a carbonyl group undergoing IR spec?
Strong sharp band around 1700cm-1
What is the IHD formula?
0.5 x [2c+2-h-x+n]
