ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS – 2

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS – 2

**The cyclodextrins have a huge range of applications in varied areas of drug delivery and pharmaceutical industry because of their characteristic ability of complexation and other versatile characteristics.

** Cyclodextrins possess the ability to form inclusion Complexes with varied drug molecules by taking up a drug molecule in their cavity.

** The factors favouring complex formation are release of enthalpy rich water molecules from the cavity and other non-covalent interactions like electrostatic interactions, Van der Waal's interactions, hydrophobic interactions, hydrogen bonding, release of conformational strain and charge transfer interactions.

** Methods to monitor the physicochemical changes (like changes in conductance or pH etc.) occurring after the formation of inclusion complexes are applied to study the mentioned changes of the aqueous complexation media.

** We have thoroughly discussed how to increase the efficiency of formation of complexes.

** Non-conventional cyclodextrin complexes gain more importance in the aspects of drug solubilisation by means of molecular aggregation.

 
ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS – 2

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS - 1

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS - 1

**Cyclodextrins first discovered by French scientist named A. Villiers, are known as structurally related group of naturally occurring products formed during bacterial digestion of cellulose.

** The glucopyranose having the chair conformation is the reason cyclodextrins have a truncated cone shape rather than perfect cylindrical shape.

** The physical state of all three cyclodextrins is crystalline and they exist as white powder. CDs donot have a sharp melting point, however they begin to decompose from temperatures 200 °C and above.

** Pharmaceutically important cyclodextrin derivatives encompass the hydroxypropy1 derivatives of beta and y-cyclodextrin. the randomly methylated Beta-cyclodextrin, sulfobutylether Beta-cyclodextrin, and the branched cyclodextrins such as glucosy1- Beta -

*** cyclodextrin.

** The most intriguing property of cyclodextrins is these molecules are able to form solid inclusion complexes also known as host-guest complexes with a very large range of solid, liquíd and gaseous compounds by following a molecular complexation protocol.

** The most widely known pharmaceutical application of cyclodextrins is their ability to enhance the stability, solubility, bioavailability and safety of drug molecules. 

** These characteristic properties of cyclodextrins or their derivatives make them appropriate for applications in analytical chemistry, the pharmaceutical industry, agriculture, in development of food flavours and toilet articles.


 
ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CYCLODEXTRINS - 1

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- BONDS WEAKER THAN COVALENT- ADDITION COMPOUNDS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- BONDS WEAKER THAN COVALENT- ADDITION COMPOUNDS

Supramolecular chemistry is a highly interdisciplinary field of science covering the chemical, physical, and biological feature of the organised chemical species of greater complexity than molecules themselves, which are held together and organized by means of intermolecular (non-covalent) binding interactions. 

**The energy of these non-covalent interactions is much smaller than 200-400 kJ mol¹ which is typical for covalent chemical bonds. 

**In addition to relatively strong ion-ion electrostatic interactions of ca. 100-350 kJ mol¹ and hydrogen bonding ca. 10-120 kJ mol¹, they include much smaller London dispersion forces, ion-induced dipole and dipole-dipole interactions that are in the range of 5-50 kj mol¹.

**The supramolecular chemistry generally concerns non-covalent bonding interactions.such as ion-ion interactions, ion-dipole interactions, dipole-dipole interactions hydrogen bonding, cation-π interactions, anion-π interactions, π-π interactions, closed shell interactions, van der Waals forces, crystal close packing and closed shell interactions. 

**The term 'non-covalent' encompasses an enormous range of attractive and repulsive effects.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- BONDS WEAKER THAN COVALENT- ADDITION COMPOUNDS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

**Tautomers are isomers of a compound, which differ only in the position of the protons and electrons. The carbon skeleton of the compound is unchanged but functional groups are different's. 

**The alpha - hydrogen of carbony1 compounds is acidic, as it is connected with the alpha - carbon that is directly bound to the electron withdrawing carbony1 group. This is the main reason for the tautomerism to occur. 

**The acidifies of these alpha-hydrogen atoms is enhanced if an electron withdrawing group is attached to the alpha -carbon atom. 

**The establishment of equilibrium may be catalyzed by both acids and bases. Through suitable means, such as by fractional crystallization or careful distillation in the absence of any acid and any base, the keto and the enolic form may be separated from each other.

** It is generally difficult to say which is the labile form, since very often a slight change in the conditions, e.g., temperature, solvent, shifts the equilibrium from keto to enol or vice versa. 

**Many scientists have suggested various forms and theories of tautomerism and this module discusses an exhaustive list of some different types of tautomerism.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- TAUTOMERISM

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS

**Greater is the delocalization of the charge, greater is the stability. Electron donating groups (+I, +M and +H) hence, stabilize electron deficient species like carbocation and free-radicals. On the other hand, Electron withdrawing groups (-I and -M) hence, stabilize electron rich species i.e, carbanions. 

**In a molecule having an electronegative atom joined directly to H atom, the acidity is affected by Ease of Deprotonation and Stability of conjugate base. 

**Both these conditions are enhanced by introducing electron withdrawing groups (-M, -H or -I )and decreased by electron donating groups (+I, +M, +H). Remember that the second condition is more dominant one than the first to arrive to the conclusion. Hence if two are opposing, rely on the second one. 

**Hence, electron donating groups (+I, +M, +H) increase the basicity; and electron withdrawing groups (-I, -M) decrease the basicity. 

**An electron releasing substituent like -CH³ increases the basicity of aniline and an electron-withdrawing substituent like-X or -NO² decreases the basicity. 

**Ortho/meta/para directive influence in electrophilic substitution of substituted benzene is affected by the electronic effects of the substituent. 

**All ortho/para directing groups are activating except halogens. On the other hand, all electron withdrawing groups are deactivating.

  ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- APPLICATIONS OF ELECTRONIC EFFECTS