General aspects of chemical structure and reactivity of organic compounds

Сентябрь 8, 2022

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General aspects of chemical structure and reactivity of organic compounds

Содержание

2. General aspects of chemical structure and reactivity of organic compounds Lecture №1
3. Chemical bonding and mutual atoms’ influence in organic molecules
4. Electronic configuration of carbon atom in organic molecules ground state excited state
5. Atomic orbitals The orbital is a region of space where the probability of finding an electron
6. Hybridization of orbitals Hybridization is the process of atomic orbitals alignment in form and energy.
7. sp3-Hybridization tetrahedral configuration
8. sp2-Hybridization planar configuration
9. sp-Hybridization linear configuration
10. Chemical bonds in organic compounds Covalent bonds σ - bond π - bond
11. Conjugation Conjugation is the formation of delocalized electronic cloud in molecule as a result of p-orbitals
12. π,π-Conjugation butadiene-1,3
13. р,π-Conjugation methyl vinyl ether
14. Aromaticity benzene A molecule can be aromatic only if it has a planar cyclic system of
15. Inductive effect Inductive effect (I) is the shifting of electrons in a σ-bond in response to
16. Mesomeric effect Mesomeric effect (М) is the shifting of electron density caused by a substituent in
17. Electron donors (D) and electron withdrawers (W)
18. Spatial structure of organic compounds
19. Isomerism of organic compounds Isomers are the compounds which have the same composition but different sequence
20. Stereoisomerism Stereoisomers are the compounds that have the same order of atoms attachment but differ only
21. Configuration is the arrangement of atoms and groups in space without regard to arrangements that differ
22. Chirality Chirality is the property of the object to be nonsuperposable with its mirror image. The
23. Enantiomers Enantiomers are the stereoisomers, the molecules of which relate to each other as an object
24. Fischer projections Spatial formulas Fischer projections Rules the carbon chain is disposed vertically (with the principle
25. D,L-Nomenclature Glyceraldehyde is the configurational standard. Fischer projection writes in “standard view”. We can do the
26. R,S-Nomenclature The least substituent near the chiral center must lie at the bottom of the Fischer
27. Diastereomers Diastereomers are the stereoisomers that are not mirror images of one another. they have different
28. meso Compounds A meso compound is an optically inactive achiral stereoisomer containing chiral centers. L-tartaric acid
29. Acidity and basicity of organic compounds
30. Acidity and basicity are the key notions, determining many fundamental physico-chemical and biochemical properties of organic
31. Brønstedt-Lowry concept J.-N. Brønstedt Т. М. Lowry An acid is a neutral molecule or an ion
32. Brønstedt acids Acidic site is a part of molecule that involves hydrogen together with an atom
33. Brønstedt bases Basic site is a heteroatom with a lone-pair of electrons or a π-bond which
34. Comparison the acidity The more stable is an anion, the stronger is an acid! The factors
35. The influence of atom nature in acidic site СН NH ОН SH СН NH ОН SH
36. The influence of substituents effects inductive effect mesomeric effect Acidity increase Acidity increase
37. Comparison the basicity The more stable is an cation and the more available a lone-pair of
38. The influence of atom nature in the basic site S О N The influence of substituents
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General aspects of chemical structure and reactivity of organic compounds
Lecture №1

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Chemical bonding and mutual atoms’ influence in organic molecules

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Electronic configuration of carbon atom in organic molecules
ground state
excited state

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Atomic orbitals
The orbital is a region of space where the probability

of finding an electron is large, above 95% of its time.

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Hybridization of orbitals
Hybridization is the process of atomic orbitals alignment in

form and energy.

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sp3-Hybridization
tetrahedral configuration

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sp2-Hybridization
planar configuration

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sp-Hybridization
linear configuration

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Chemical bonds in organic compounds
Covalent bonds
σ - bond π -

bond

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Conjugation
Conjugation is the formation of delocalized electronic cloud in molecule as

a result of p-orbitals overlap.
π,π-Conjugation is the type of orbital interaction when the p-orbitals are delocalized over the entire π system.
p,π-Conjugation is the overlap of a p-orbital on an atom adjacent to a double bond.

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π,π-Conjugation
butadiene-1,3

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р,π-Conjugation
methyl vinyl ether

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Aromaticity
benzene
A molecule can be aromatic only if it has a planar

cyclic system of conjugation with a p-orbital on each atom and only if the p-orbital system contains (4n+2) π-electrons, where n is an integer (0, 1, 2, 3, etc.).

Слайд 15

Inductive effect
Inductive effect (I) is the shifting of electrons in a

σ-bond in response to electronegativity of nearby atoms.
present in any polar molecule;
decrease and fade after 2-3 bonds.
СН3→СН2→Сl CH3←CH2←MgCl

-I-effect

+I-effect

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Mesomeric effect
Mesomeric effect (М) is the shifting of electron density caused

by a substituent in conjugation system through p-orbital overlap.
present only in conjugation systems;
distribute throughout the conjugated system.

+М-effect

-М-effect

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Electron donors (D) and electron withdrawers (W)

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Spatial structure of organic compounds

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Isomerism of organic compounds
Isomers are the compounds which have the same

composition but different sequence of atoms or their location in space, therefore have different properties.

Isomers

Structural

Spatial

Skeleton isomers

Positional isomers

Functional isomers

Geometrical

Optical

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Stereoisomerism
Stereoisomers are the compounds that have the same order of atoms

attachment but differ only in the arrangement of their atoms or groups in space.

Stereoisomers

Configurational

Conformational

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Configuration is the arrangement of atoms and groups in space without

regard to arrangements that differ only due to rotation about one or more single bonds.
Carbon atom configurations

Configuration of molecules

tetrahedral planar linear

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Chirality
Chirality is the property of the object to be nonsuperposable with

its mirror image.
The simple example of chirality is presence the chiral center in molecule.
It may be carbon atom with four different atoms or groups - asymmetric carbon atom (*С).
Such molecules have optical activity – they rotate the plane of polarized light.
Types of isomers:
enantiomers
diastereomers

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Enantiomers
Enantiomers are the stereoisomers, the molecules of which relate to each

other as an object and its nonsuperposable mirror image.
enantiomers have the same physical and chemical properties;
enantiomers have optical activity.

Enantiomers of glyceraldehyde

Racemate is a mixture containing equal amounts of both enantiomers. Racemic mixture is optically inactive.

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Fischer projections
Spatial formulas Fischer projections
Rules
the carbon chain is disposed

vertically (with the principle group at the top);
substituents on the horizontal line lie in front of the plane, on vertical line– behind the plane of the paper;
two interchanges do not alter the initial configuration;
the rotation of projection through 180o in the plane of the paper do not alter the initial configuration.

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D,L-Nomenclature
Glyceraldehyde is the configurational standard.
Fischer projection writes in “standard

view”. We can do the interchanges or rotate the projection through 180o to achieve the “standard view”.
If the group lies on the left side we name it as levorotatory enantiomer (L). If the group lies on the right side we name it as dextrorotatory enantiomer (D).

L-alanine D-lactic acid

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R,S-Nomenclature
The least substituent near the chiral center must lie at

the bottom of the Fischer projection.
Atoms attached directly to the chiral center are first arranged according to decreased atomic number.
If the remaining three groups are arranged clockwise, the configuration is symbolized by R. If they form a counterclockwise array, the configuration is symbolized by S.

L-lactic acid

(S)-lactic acid

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Diastereomers
Diastereomers are the stereoisomers that are not mirror images of one

another.
they have different physical and chemical properties.

If a molecule has n chiral centers, the total number of stereoisomers will be N = 2n.

Diastereomers

Enantiomers

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meso Compounds
A meso compound is an optically inactive achiral stereoisomer containing

chiral centers.

L-tartaric
acid

D-tartaric
acid

meso-tartaric
acid

plane of
symmetry

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Acidity and basicity of organic compounds

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Acidity and basicity are the key notions, determining many fundamental physico-chemical

and biochemical properties of organic compounds.

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Brønstedt-Lowry concept
J.-N. Brønstedt
Т. М. Lowry
An acid is a neutral molecule or

an ion that can donate a proton.

A base is a neutral molecule or an ion that can accept a proton.

АН + :В = А- + ВН+
acid base conjugate conjugate
base acid

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Brønstedt acids
Acidic site is a part of molecule that involves hydrogen

together with an atom attached to it.

Acids

СН-acids

ОН-acids

SН-acids

NН-acids

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Brønstedt bases
Basic site is a heteroatom with a lone-pair of electrons

or a π-bond which are capable to accept a proton.

Bases

n-bases

π-bases

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Comparison the acidity
The more stable is an anion, the stronger is

an acid!
The factors which influence the stability of conjugate bases:
electronegativity and polarizability of the atom in the acidic site;
delocalization of a negative charge due to the effect of substituens in a molecule;
solvation effects.

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The influence of atom nature in acidic site
СН NH ОН
SH

СН NH ОН SH

The electronegativity increase
At
omi
c
s
i
z
e
i
nc
r
ea
s
e

Acidity increase

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The influence of substituents effects
inductive effect
mesomeric effect
Acidity increase
Acidity increase

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Comparison the basicity
The more stable is an cation and the more

available a lone-pair of electrons, the stronger is an base!
The factors which influence the stability of conjugate acids is the same but they act in the opposite direction:
.

n-bases

π-bases

Basicity increase

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The influence of atom nature in the basic site
S О

N
The influence of substituents effects

Basicity increase

General aspects of chemical structure and reactivity of organic compounds

Содержание

General aspects of chemical structure and reactivity of organic compoundsLecture №1

Chemical bonding and mutual atoms’ influence in organic molecules

Electronic configuration of carbon atom in organic moleculesground stateexcited state

Atomic orbitalsThe orbital is a region of space where the probability

Hybridization of orbitalsHybridization is the process of atomic orbitals alignment in

sp3-Hybridizationtetrahedral configuration

sp2-Hybridizationplanar configuration

sp-Hybridizationlinear configuration

Chemical bonds in organic compoundsCovalent bonds σ - bond π -

ConjugationConjugation is the formation of delocalized electronic cloud in molecule as

π,π-Conjugationbutadiene-1,3

р,π-Conjugationmethyl vinyl ether

AromaticitybenzeneA molecule can be aromatic only if it has a planar

Inductive effectInductive effect (I) is the shifting of electrons in a

Mesomeric effectMesomeric effect (М) is the shifting of electron density caused

Electron donors (D) and electron withdrawers (W)

Spatial structure of organic compounds

Isomerism of organic compoundsIsomers are the compounds which have the same

StereoisomerismStereoisomers are the compounds that have the same order of atoms

Configuration is the arrangement of atoms and groups in space without

ChiralityChirality is the property of the object to be nonsuperposable with

EnantiomersEnantiomers are the stereoisomers, the molecules of which relate to each

Fischer projections Spatial formulas Fischer projectionsRules the carbon chain is disposed

D,L-Nomenclature Glyceraldehyde is the configurational standard. Fischer projection writes in “standard

R,S-Nomenclature The least substituent near the chiral center must lie at

DiastereomersDiastereomers are the stereoisomers that are not mirror images of one

meso CompoundsA meso compound is an optically inactive achiral stereoisomer containing