STEREOCHEMICAL THEORY OF OLFACTIONThe Stereochemical theory of olfaction statesthat a molecules particular smell is due to a lockand key mechanism by which a scent moleculefits into olfactory receptors in the nasal epithelium.Stereochemistry, a subdiscipline of chemistry, involves the studyof the relative spatial arrangement of atoms that form the structureof molecules and their manipulation. An important branch ofstereochemistry is the study of chiral molecules.Stereochemistry is also known as 3D chemistry because the prefix"stereo-" means "three-dimensionality".The study of Stereochemistry focuses on stereoisomers.stereoisomers.are isomeric molecules that have the samemolecular formula and sequence of bonded atoms (constitution),but that differ only in the three-dimensional orientations of theiratoms in space. This contrasts with structural isomers, which sharethe same molecular formula, but the bond connections and/or theirorder differ(s) between different atoms/groups. In stereoisomers,the order and bond connections of theconstituent atoms remain thesame, but their orientation in space differsThere are 2 types of stereoisomers:
ENANTIOMERSIn chemistry, an enantiomer is one of two stereoisomers that aremirror images of each other that are non-superposable (notidentical), much as ones left and right hands are the same exceptfor opposite orientation.
S-lactic acid and L-lactic acidChiralityA chiral molecule is a type of molecule that has a non-superposable mirror image. The feature that is most often the causeof chirality in molecules is the presence of an asymmetric carbonatom.In chemistry, chirality usually refers to molecules. Two mirrorimages of a chiral molecule are called enantiomers or opticalisomers.Diastereomer:Diastereomers (sometimes called diastereoisomers) arestereoisomers that are not enantiomers. Diastereomerism occurswhen two or more stereoisomers of a compound have differentconfigurations at one or more (but not all) of the equivalent(related) stereocenters and are not mirror images of each other. L-tartaric acid
D-tartaric acid DIASTEREOMERSOlfaction is the sense of smell. This sense is mediated byspecialized sensory cells of the nasal cavity of vertebrates, and, bysensory cells of the antennae of invertebrates.OLFACTION depends on the structure of particular molecule.
Human olfactory system. 1: Olfactory bulb 2: Mitral cells 3:Bone 4: Nasal epithelium 5: Glomerulus (olfaction) 6:Olfactory receptor cellsDetection of odors 1.The initial detection of odors takes place at the back of the nose in a small region known as the olfactory epithelium. 2.Dissolved molecules interact with specialized receptors called odorant-binding proteins. (Odorants are molecules that stimulate the olfactory receptors.)
3.The binding of the molecules to these receptors initiate an electrical signal that transmits to the olfactory bulbs and higher brain centers for processing of the olfactory information. 4.To distinguish the smell, the brain must then determine the precise combination of receptors that are activated by a particular odor.SO, olfactiondepends on the structure of particular molecule.Odorants must be volatileOdorants are nonionic compounds,It must be volatile atambient temperature, so that the molecule can reach thenose. It must interact with the protein odorant receptorsites in the nose.
VOLATILE OILSVolatile oils are the odorous principles found invarious plant parts. STEREOISOMERS, VOLATILE OILS AND OLFACTION: 1. (VOLATILE OIL) STEREOISOMER(CONSTITUENT OF Orange and Lemon) Smells differently
2. (VOLATILE OIL)(+ )Carvone smells like Mint and(- )Carvone smells like Caraway3.One stereoisomers of PHENANDRENE smellslikeeucalyptus andother smell likefennel. α-Phellandrene(Smells like Eucalyptus) β-phellandrene(smells like fennel)Because molecules of volatile oils bind to specific proteinsin nasal cavity called olfactory receptors .Each olfactory
receptor can only bind molecules that have acomplementary shape, just as right hand will only fit intoa right-handed glove, and thats how brain distinguishesbetween the scent of the the two stereoisomer moleculesbind to olfactory receptors on different nerve endings innose.