spectroscopy

what is the electromagnetic spectrum?

spectroscope technique that provides snapshots of a molecule as different types of E affect a molecule differently

what are the types of spectroscopy?

• IR: obtains functional groups present

• nuclear magnetic resonance spectroscopy (NMR): obtains the specific arrangement of all C and H atoms in the compound

• UVF and visible spectroscopy (UV-VIS): obtains any conjugated 𝜋 system present in the compound

what is the mid-IR region?

• 4000-6000 cm^-1
• where most organic molecules absorb IR energy

what are vibrations?

atoms are in constant motion and move like balls at the end of a spring

what are IR radiations?

• have just the right amount of energy to stretch/bend a bond, but not break it
• results in the molecule absorbing energy, resulting in an absorption band at that frequency

what are the types of atom movements?

symmetric/asymmetric stretching, wagging, twisting, rocking, scissoring

what are the IR trends?

• atomic mass: frequency/wave # increases with increasing mass
• bond order: frequency/wave # increases with increasing bond #

what is the frequency of O-H?

3650-2500

what is the frequency of N-H?

3500-3150

what is the frequency of C-H?

3300-2850

what is the frequency of C-C?

1200

what is the frequency of C=C?

1660

what is the frequency of C≡C?

2200

what is the frequency of amides?

1681

what is the frequency of ketones?

1715

what is the frequency of carboxylic acids?

1722

what is the frequency of aldehydes?

1727

what is the frequency of esters?

1745

what is the frequency of acid chlorides?

1806

what is the frequency of acid anhydrides?

1827 and 1766

what is NMR spectroscopy?

• excite protons/carbon atomics so that their spins align against a magnetic field
• output: range of frequencies that correspond to the type of proton/C
• determines exact structure of a compound and impurities

what is the information obtained from an NMR spectroscopy?

• shift: what type of proton we have; strongly influenced by the surrounding electron density
• integral: how many protons in relation to other peaks; shows ratio
• splitting: what the proton is next to

what are NMR shifts?

• different proton will contain different sets of shifts
• ranges will vary slightly depending on the molecule
• plotted on a scale of ppm derived from the frequency that the particular proton aligns at

what does an equivalent proton show up as?

a single peak

what is splitting?

• tells us the relationship between adjacent (vicinal) protons

• doublet, triplet, quartet

• if next to 2 different types of protons, you get more complex peaks that may be 2 sets of doublets

• useful in determining the location of groups on an aromatic and cyclohexane ring

what is beer's law?

• concentration is proportional to absorbance intensity
  A = ɛbc

what is UV-VIS spectroscopy?

• compounds absorb light through the excitation of electrons: for a compound to absorb light, it needs accessible electrons

• compounds with 𝜋 bonds tend to absorb UV light: the more double bonds, the more intense the UV absorption

• conjugation increases absorbance intensity

• can obtain AUC and concentration from peak data

what is fluorescence?

• certain molecules can be excited by UV/visible light, but will emit radiation at a longer wavelength

• electrons are excited but then relax in segments, leading to a different emission

• some drugs themselves are fluorescent because they have extended 𝜋 systems

• not predictable

what are the uses of fluorescence?

• to measure the binding of a drug to a receptor/target
• detecting fluorescent impurities