Chemical Reactivity

-
Chemical Reactivity

Organic chemistry encompasses a very large number of compounds ( many millions ), and our previous discussion and illustrations have focused on their structural characteristics. Now that we can recognize these actors ( compounds ), we turn to the roles they are inclined to play in the scientific drama staged by the multitude of chemical reactions that define organic chemistry.
We begin by defining some basic terms that will be used frequently as this subject is elaborated.
    Chemical Reaction: 
    A transformation resulting in a change of composition, constitution and/or configuration of a compound ( referred to as the reactant or substrate ).
    Reactant or Substrate:
     The organic compound undergoing change in a chemical reaction. Other compounds may also be involved, and common reactive partners ( reagents ) may be identified. The reactant is often ( but not always ) the larger and more complex molecule in the reacting system. Most ( or all ) of the reactant molecule is normally incorporated as part of the product molecule.
    Reagent: 
    A common partner of the reactant in many chemical reactions. It may be organic or inorganic; small or large; gas, liquid or solid. The portion of a reagent that ends up being incorporated in the product may range from all to very little or none.
    Product(s);
     The final form taken by the major reactant(s) of a reaction. 

    Reaction Conditions 

    The environmental conditions, such as temperature, pressure, catalysts & solvent, under which a reaction progresses optimally. Catalysts are substances that accelerate the rate ( velocity ) of a chemical reaction without themselves being consumed or appearing as part of the reaction product. Catalysts do not change equilibria positions.

    Chemical reactions are commonly written as equations:

Comments

Post a Comment

Popular posts from this blog

What Is Melting Points

-
Image
Most organic compounds have melting points below 200 ºC. Some decompose before melting, a few sublime, but a majority undergo repeated melting and crystallization without any change in molecular structure. When a pure crystalline compound is heated, or a liquid cooled, the change in sample temperature with time is roughly uniform. However, if the solid melts, or the liquid freezes, a discontinuity occurs and the temperature of the sample remains constant until the phase change is complete. This behavior is shown in the diagram on the right, with the green segment representing the solid phase, light blue the liquid, and red the temperature invariant liquid/solid equilibrium. For a given compound, this temperature represents its melting point (or freezing point), and is a reproducible constant as long as the external pressure does not change. The length of the horizontal portion depends on the size of the sample, since a quantity of heat proportional to the heat of fusion must be...
Read more

What Is Atomic And Molecular Orbitals

-
Image
A more detailed model of covalent bonding requires a consideration of valence shell atomic orbitals. For second period elements such as carbon, nitrogen and oxygen, these orbitals have been designated 2 s , 2p x , 2p y   & 2p z . The spatial distribution of electrons occupying each of these orbitals is shown in the diagram below.   Very nice displays of orbitals may be found at the following sites: J. Gutow, Univ. Wisconsin Oshkosh R. Spinney, Ohio State  M. Winter, Sheffield University The valence shell electron configuration of carbon is 2 s 2 , 2p x 1 , 2p y 1  & 2p z 0 . If this were the configuration used in covalent bonding, carbon would only be able to form two bonds. In this case, the valence shell would have six electrons- two shy of an octet. However, the tetrahedral structures of methane and carbon tetrachloride demonstrate that carbon can form four equivalent bonds, leading to the desired octet. In order to explain this covalent bonding,...
Read more

Uses OF Alkynes In Nature And Medicine

-
Alkynes in nature and medicine According to Ferdinand Bohlmann, the first naturally occurring acetylenic compound, dehydromatricaria ester, was isolated from an Artemisia  species in 1826 . Polyynes, a subset of this class of natural products, have been isolated from a wide variety of plant species, cultures of higher fungi, bacteria, marine sponges, and corals.  Some acids like  tariric acid  contains an alkyne group. Diynes and triynes, species with the linkage RC ≡ C-C ≡ CR' and RC ≡ C-C ≡ C-C ≡ CR' respectively, occur in certain plants ( Ichthyothere , Chrysanthemum ,  Cicuta ,  Oenanthe  and other members of the  Asteraceae  and  Apiaceae  families).  Some examples are  cicutoxin , oenanthotoxin ,  falcarinol  and  carotatoxin . These compounds are highly bioactive, e.g. as  nematocides .  1-Phenylhepta-1,3,5-triyne is illustrative of a naturally occurring triyne. Alkynes occ...
Read more