Beer Ambert Law

Spectroscopy || Beer- Lambert’s Law

UV Spectroscopy

https://www.youtube.com/watch?v=NhmSGCqVR7k&t=479s&ab_channel=Knowbee

-basically confirms the presence of a conjugated system if there is any absorbance at all in the UV range

e.g. β-Carotene, porphyrin, tryptophan

IR Spectroscopy

Introduction to infrared spectroscopy | Spectroscopy | Organic chemistry | Khan Academy

Bonds as springs | Spectroscopy | Organic chemistry | Khan Academy

where ~v is wavenumber (1/wavelength)

-only vibrations that produce a change in dipole moment are detected by IR spectroscopy

-dipole moment = charge x distance

–large dipole moments produce larger peaks (more absorbance)

-smaller dipole moments produce smaller peaks

For the MCAT:

Signal characteristics – wavenumber | Spectroscopy | Organic chemistry | Khan Academy

IR spectra for hydrocarbons | Spectroscopy | Organic chemistry | Khan Academy

-ketones produce large signals due to large dipole moment

-alkenes produce smaller signals due to smaller dipole moment

–completely symmetrical alkenes produce no signal due to zero dipole moment

Signal characteristics – intensity | Spectroscopy | Organic chemistry | Khan Academy

-hydrogen bonding in solution produces broad peaks (-OH, -NH)

Signal characteristics – shape | Spectroscopy | Organic chemistry | Khan Academy

-for a primary amine (H2NR), the two hydrogens conncected to the nitrogen give two different signals next to eachother due to (A) symmetric streching and (B) asymmetric stretching

-also happens to anhydrides for the same reason

Symmetric and asymmetric stretching | Spectroscopy | Organic chemistry | Khan Academy

Factors effecting IR frequency absorption:

1. Inductive Effect: increases energy (bc/ brings more lone pair electons into bond, thus increasing k)
2. Resonance: decreases energy (bc/ kicks electrons out of bound, thus decreasing k)

-groups that allow a carbonyl bond to kick its pi electrons to the oxygen will decrease the bond energy

3. Hydrogen bonding (i.e. O-H, N-H peaks): makes broad peak
4. larger dipole moments produces larger peak

-completely symmetrical bonds produce no peak

IR signals for carbonyl compounds | Spectroscopy | Organic chemistry | Khan Academy

IR spectra practice | Spectroscopy | Organic chemistry | Khan Academy

UV/Vis Spectroscopy

UV/Vis spectroscopy | Spectroscopy | Organic chemistry | Khan Academy

Absorption in the visible region | Spectroscopy | Organic chemistry | Khan Academy

Conjugation and color | Spectroscopy | Organic chemistry | Khan Academy

Nuclear Magnetic Resonance

NMR spectroscopy visualized

magnetic atoms: odd number of proton and/or odd number of neutrons

Introduction to NMR Spectroscopy Part 1

Introduction to NMR Spectroscopy Part 2

-during NMR, a RF pulse brings the proton from the lower energy alpha spin state to the higher energy beta spin state

Number of Signals in NMR 1st Aspect of NMR

Shifting of Signals in NMR 2nd Aspect of NMR Part 1

Shifting of Signals in NMR 2nd Aspect of NMR Part 2 Anisotropy

Aromatic ring:

-aromatic rings and double bonds deshield protons (shift downfield)

-triple bonds shield protons (shift upfield)

Shifting of Signals in NMR 2nd Aspect of NMR Part 3

Integration of Signals in NMR 3rd Aspect of NMR

Splitting of Signals in NMR   4th Aspect of NMR Part 1

Splitting of Signals in NMR   4th Aspect of NMR Part 2

Splitting of Signals in NMR  4th Aspect of NMR Part 3

Spin Spin Splitting – N+1 Rule – Multiplicity – Proton NMR Spectroscopy

Nuclear Magnetic Resonance (Advanced)

NMR Coupling Constants in Organic Chemistry

can use J values for two things:

1. to see which set of hydrogens are next to eachother
2. to see whether the hydrogens around a double bond are cis or trans

-if J values are the same, then those two sets of hydrogen are next to eachother

Splitting Diagrams NMR Organic Chemistry

Complex Splitting:

-occurs when the neighboring hydrogens are in different electronic environments

-quartet of triplets

Enantiotopic and Diastereotopic Hydrogens in Organic Chemistry

Homotopic, Enantiotopic, Diastereotopic, and Heterotopic Protons

-Hydrogens that are diastereotopic are in different chemical environments and so have different chemical shifts and thus are represented by different chemical peaks

OH and NH Signals in HNMR in Organic Chemistry

Deuterium in HNMR in Organic Chemistry