ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- INCLUSION COMPOUNDS

** An inclusion compound or an inclusion complex maybe defined as: 'A complex which comprises of one component (the host) forming a cavity. In the case of a crystal, it consists of a crystal lattice containing spaces in the shape of long tunnels or channels in which molecular entities of a second chemical species (the guest) are located. There exists no covalent bonding between the guest and host, the attraction being mainly attributed due to Van der Waals forces. ** Mylius observed Inclusion compounds for the first time in 1886. They appeared as unusual complexations occurring between hydroquinone and several volatile as compounds.

** A more convenient and workable classification, utilized in this review, is based upon the organization of inclusion compounds by their structure and properties as follows: 1 Polymolecular inclusion compounds -Channel-like spaces -Cage-like spaces 2. Monomolecular inclusion compounds 3. Products of the blue-iodine reaction 4. Macromolecular inclusion compounds.

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CROWN ETHERS, COMPLEXES AND CRYPTANDS

ORGANIC CHEMISTRY- I (NATURE OF BONDING AND STEREOCHEMISTRY)- CROWN ETHERS, COMPLEXES AND CRYPTANDS


** Crypts and crown ethers constitute an important and an interesting class of complexing ligands.

** When the Nobel was conferred upon the three chemists Pederson, Cram and Lehn in 1987, the advances in host guest and supramolecular chemistry gained special attention.

** The crowns and crypts are enormously studied due to their increasing applications varied chemical and physical processes. Their use as biochemical models further draws greater interest towards them.

** Crown ethers (or crowns) are known as a group of macrocyclic polyethers. Many macropolycyclic ligands which are related to each other are also known to us and are called as 'cryptates' (or cryptands or simply, crypts)

** The two rings of cryptand provide extra strength to hold the ion. In case a regular crown ether "surrounds" an ion, a cryptand "locks it up". This ion-capturing capability of a cryptand can reach upto a hundred thousand times more than that of 18-crown-6.

** Crowns and crypts find many important applications and uses. These include preparative organic chemistry, solvent extraction, phase transfer catalysis, stabilisation of uncommon or reactive oxidation states and the promotion of other improbable reactions.

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

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

**A homoaromatic molecules showed discontinuity in the p orbital overlap due to the presence of a single sp³ hybridized atom, so we can say that those compounds where the stable configuration systems with (4n+2) π e can only be formd by bypassing One saturated sp³ hybridized carbon atom leads to homoaromaticity.

** The homotropylium cation (C8H9) is the best studied example of a homoaromatic compound. 

**Criteria for a compourd to be homoaroatic are :

#The molecule should posses one or more homoconjagative interactions. 

#A closed cyclic system must show electron delocalization.

#The member of π-electrons participating in cyclic electron delocalization should be close to 4n +2.

#No-bond homoaromatic systems should posses exceptional magnetic properties #Homoaromaticity should have resonance anergy greater than 2 leak mol¹ which leads to stabilization. 

**Classify the homoaromatic compounds depending on the type of interactions as no bond homoaromatics, sigma bond homoaromatics and homoarcmatics having transannular homoconjugative interactions. **Examples of homoaromatics including cationic, neutral and anionic homoaromatic compounds.