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MindMap Gallery Natural Medicinal Chemistry Structural Research Method-Absolute Configuration

Natural Medicinal Chemistry Structural Research Method-Absolute Configuration

This is a mind map about the structure research method of natural medicinal chemistry - absolute configuration. Absolute configuration refers to the three-dimensional structure of a compound, including the orientation of the chiral center and chiral axis.

Edited at 2024-01-16 20:29:19

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Natural Medicinal Chemistry Structural Research Method-Absolute Configuration

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Outline

structural research method

absolute configuration

How to determine absolute configuration

chiral spectroscopy

Optical rotation spectrum (ORD)

Circular dichroism (CD)

NMR method (chiral synthesis)

Aromatic ring diamagnetic shielding effect

Glycoside shift effect

X-ray single crystal diffraction method

chemical method

chiral optics

principle: Optical rotation: When left-handed circularly polarized light and right-handed circularly polarized light that make up plane polarized light pass through chiral substances, their polarization planes rotate due to their different refractive indexes (or different propagation speeds). Circular dichroism: A phenomenon caused by the different absorption coefficients of left-handed circular polarization and right-handed circular polarization in chiral substances. When irradiated with different wavelengths, the optical rotation and circular dichroism are different.

Optical rotation: • Specific optical rotation: [α]λt = α/c. l • Molecule specific rotation: [φ] = [α]λt. M/100 α: Optical rotation c: Concentration (g/mL) l: Absorption pool length (dm) M: molecular weight

Circular dichroism:• Absorption coefficient difference: Δε = θ/33 × /c. l • Molar ellipticity: [θ] ≈ 3300Δε θ: measured ellipse angle

ORD curve: [φ]×10-2-λ curve

CD curve: [θ]×10-2-λ curve

ORD spectrum

Flat type: positive, negative

Cotton effect type: simple type: only one peak and valley appears; complex type: more than two peaks and valleys

Cotton effect judgment: long wave → short wave direction, peak first and then trough, positive; long wave → short wave direction, first trough then peak, negative

CD spectrum: positive: peak; negative: valley

Exciton chiral method of CD spectrum: Positive exciton chirality: long wave direction is Cotton effect; electronic transition is right-handed; clockwise direction; Negative exciton chirality: long wave direction is -Cotton effect; electronic transition is left-handed; counterclockwise direction

Eight-zone rhythm of ORD and CD spectrum

The principle of ORD and CD measurement

Compounds with chromophores surrounding the chiral center Chiral centers can enhance sensitivity The closer to the chromophore, the greater the influence

Eight District Law

Empirical rules summarized from ORD spectrum and CD spectrum There are many empirical factors, and there is a big error between theoretical and actual measurement results.

The scope of application of the eight-zone law

Ketone group, conjugated double bond, unsaturated ketone, lactone, nitro compound Compounds that can be chemically converted into the above groups

Application of the eight-zone rule: ORD and CD of saturated ketones

Planes A, B, and C are perpendicular to each other: • The A plane is the plane along the C=O bond axis • The bond connecting C=O is on plane B • C plane division C=O is the front and rear partitions • The β-position C and its substituents must be above the B plane • C in the γ position and its substituents must be on the A plane

Be sure to consider the dominant conformations Generally, only the rear partition needs to be considered The groups on the A and B planes contribute 0 to the optical activity

NMR determination of absolute configuration (chiral synthesis)

NMR method using the diamagnetic shielding effect of aromatic rings

Mosher method Modified Mosher method MPA and other AMAs chiral reagent methods

The principle of the classic Mosher method: secondary alcohols (primary amines) form Mosher esters with (R), (S)-MTPA respectively; compare the 1H-NMR (or 19F-NMR) of (R), (S)-MTPA esters; get Δδ (Δδ = δS-δR); Δδ symbol determines the absolute configuration

NMR method using glycoside shift effect

4-O-benzoylglucopyranoside method Fucofuranoside method