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1.        Visible light forms part of the electromagnetic spectrum and extends from wavelength of approximately 400 to 750 nm.

2.        Ultraviolet (UV) radiation (of wavelength that may be exploited for analytical purposes) extends from wavelength of approximately  180 to 400 nm.

3.        The energetic states of orbitals and their electrons are quantized.

4.        The promotion of a valence electron from one orbital to another involves absorption of radiation normally in the UV or visible range of wavelengths.

5.        The energy of electromagnetic radiation =hv = hc /λ

6.        The Beer-Lambert law describes the absorption of radiation by compounds with a molar absorptivity ofε, and a concentration, c, through a path length , l, and states that A =εcl.

7.        Absorbance is unit-less quantity.  A = log10(I0 / I), where I0 is the intensity of the incident radiation and I is the intensity of the transmitted radiation.

8.        A number of different light sources may be used for UV-visible spectroscopy, such as tungsten filament, hydrogen, and deuterium lamps.

9.        Monochromators are used for wavelength selection and are based on diffraction prisms or reflection gratings.

10.    A number of photon detectors are used with UV-visible spectrometers and include photo-tubes, photo-multiplier tubes, silicon photo-diodes, and photo-voltaic cells.

11.    UV-visible spectrometers are based either on a single- or double-beam formats.  Single-beam spectrometers necessitate separate baselines to be determined with blank samples.  Double-beam spectrometers, by contrast, allow two cells to be determined – one as a blank to establish the baseline and one for the sample itself.

12.    Cuvettes may be made of quartz, glass, or plastic depending on the wavelength range over which spectra are to be run.  Quartz cuvettes must always be used for wavelength ranges  ＜360 nm.

13.    A shift in the λmax from a shorter to a longer wavelength is known as a bathochromic shift.

14.    A shift in the λmax from a longer to a shorter wavelength is known as a hypsochromic shift.

15.    The rules for conjugated compounds

Nuclear magnetic resonance spectroscopy

1、Nuclear magnetic resonance (NMR) is an instrumental technique based on monitoring how spinning nuclei with magnetic dipoles interact with applied magnetic fields and absorb radiation.

2、Nuclei can only absorb energy from an electromagnetic field when they possess a magnetic dipole moment.

3、Magnetic dipoles of nuclei interact with a static magnetic field, H, by precessing in a manner analogous to a gyroscope spinning in a gravitational field.

4、Frequencies of electromagnetic radiation, r, that will be absorbed may be predicted by: r = ΔE / h, and are known as Larmor frequencies.

5、Frequencies of alternating magnetic fields range from a few MHz to 900 MHz or more.

6、High resolution NMR is more versatile than low-resolution NMR spectroscopy and finds applications for structural identification of unknown compounds.

7、The resonance of a number of differing nuclei may be exploited, although proton (1H) NMR spectroscopy is the most widely used.

8、A feature of high resolution NMR spectroscopy is the splitting of peaks due to interactions with nuclei on neighbouring functional groups; this is known as the fine structure of the spectrum.

9、The chemical shift, δ, describes the change in frequency of the magnetic field that may be applied in order to bring specific nuclei into resonance with an applied field.

10、Chemical shifts are often measured with respect to standards.  The protons of tetramethylsilane are normally used for this purpose.  The peak due to TMS is normally designed aδ= 0.

11、Spin-spin coupling describes the interaction of protons in two or more chemical environments to give rise to the fine structure of the NMR spectrum.

12、If a functional group, R, with protons undergoes spin-spin coupling with another group possessing N protons, then the NMR peak due to the protons on the R group will be split into a multiplet with N + 1 peaks.

13、Integration peaks describe the relative areas under NMR peaks and this may be related to the number of protons in a particular chemical environment.

Mass Spectrometry

1、Mass spectrometry is an instrumental technique relying on separating gaseous charged ions according to their mass-to-charge ratios.

2 、 Sample inlet systems are designed to introduce a sample into the mass spectrometer with as little a loss in the quality of vacuum as possible.

3 、 The three most commonly used inlet systems used in mass spectrometry are : (1) batch inlet; (2) direct probe; and (3) chromatographic type inlet systems.

4 、 Mass analysers disperse ionized sampling according to differences in their mass-to-charge (m/z) ratios as they emerge from the ionization source or chamber.

5 、There are a number of different ionization chambers routinely being used and these include: electron impact (EI), chemical ionization(CI), fast atom bombardment (FAB), secondary ion mass spectrometer (SIMS), field ionization / desorption, laser desorption, inductively coupled plasma (ICP), and atmospheric pressure electron impact ionization sources, and etc.

6 、There are a number of differing mass analysers routinely used and these include:magnetic sector analysers, double focusing analysers, quadrupole mass analysers, ion cyclotron resonance ion trap and time-of-flight mass analysers.

7 、Quadrupole mass spectrometers contain four rods: each rod is electrically connected to its neighbour.  A dc potential is applied between the two pairs of rods.  An ac potential is superimposed on these and potentials are used to separate ions according to their m/z ratios.  Ions of individual m/z ratios are sequentially allowed to pass through the space enclosed by the four rods and so onto the mass analyser.

8 、Electron impact detectors are widely used as ion detectors within mass spectrometry and may consist of electron multiplier detectors or continuous dynode electron multipliers.  Other ion detectors include:  Faraday cup detectors, and scintillation detectors etc.

Infrared (IR) Spectrometry

1、IR radiation forms part of the electromagnetic spectrum and covers a range of wavelengths from approximately 0.8 to 1000 um.

2、IR absorption occurs via the stimulation of a number of molecular vibrations including rocking, wagging, scissoring, and twisting motions.

3、IR absorption follows the Beer-Lambert law.

4、IR spectra are normally presented with the Y-scale representing transmittance (or sometimes percentage transmission) and the X-scale in terms of wavenumber cm-1 .

5、Vibrational transitions in molecules cause absorption in the infrared  region of the electro- magnetic spectrum.

 6、Vibrational spectra give information about the functional groups in molecule, and the observed group frequencies are affected by molecular interactions such as hydrogen bonding.

7、Infrared instruments include a radiation source, a means of analyzing the radiation and a detection and data processing system.  Additionally, sampling methods to deal with gases, liquids, solids, and microsamples and mixtures are available.

8、Specific functional groups such as C-H, C=C, C-N, NO2 and OH groups give rise to absorptions at characteristic wavenumbers and these allow compounds to be matched by “fingerprinting ” approaches with reference to data libraries.

9、A number of IR sources are used with IR instruments and include Nernst glower, globar, tungsten filament, and laser sources etc.

10、Detectors used in IR spectrometers include thermal, pyroelectric, and photoconducting based devices.

11、IR spectrometers operate either via dispersive grating or multiplex priciples.

12、Multiplex instruments employ an interferometer, the Michelson – type interferometer is the most commonly encountered design.  Multiplex instruments rely on de-convoluting the signal by a mathematical treatment of the data such as a Fourier transform.  Many IR spectrometers are simply known as Fourier transform IR (or FTIR) spectrometers.

13 、The group frequencies observed in an infrared spectrum of organic compounds are useful indicators of molecular structure.  Inorganic materials may also give specific infrared bands characteristic of their structure and bonding.

14 、The intensity of infrared absorbance obeys the Beer-Lambert and may be used for quantitative analysis.