Organic Chemistry Chapter 1 Introduction to organic chemistry 1.
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Organic Chemistry Chapter 1Introduction to organic chemistry *Introduction to organic chemistry History:Earlier in the eighteenth century it was believed that in order to produce compounds by living cells, a vital force was needed.These compounds were classified as organic compounds.A german chemist, Friedrich Woehler in 1828 has shown this belief was incorrect*How did Woehler end this belief?He prepared urea, a compound normally found in both blood and urine, by heating a solution of ammonium cyanate, which is considered an inorganic compound:NH4CNO heat NH2-CO-NH2*Later on many other organic compounds were produced in the laboratory.This has led to the subdivision of chemistry into 2 parts:OrganicInorganic*Organic ChemistryDefinition: With the simplest definition, organic chemistry is known as the chemistry of carbon compounds.*What makes Carbon so special to give it a whole branch of chemistry and place all other elements in the other branch?Carbon is unique in that it forms covalent bonds to other carbon atoms as well as to other elements.There are millions of organic compounds known today*Importance of organic chemistryIts importance comes from its association with all living matter in both plants and animalsExamples:Proteins, carbohydrates, lipids, hormones, vitamins, enzymes, and many other drugs are organic compounds.*Comparison of organic and inorganic compounds*organicinorganicFlammableyesnoMelting pointlowhighBoiling pointlowhighSolubility in waterNo (most)yesSolubility in nonpolar liquidsyesnoTypes of bondingcovalentionicReactions occur betweenmoleculesionsAtoms per moleculesmanyfewstructurecomplexsimpleElectrolytenoyesCarbon and the Covalent BondC usually forms covalent bonds with other atoms by sharing electrons.Covalent bond: an evenly strong bond formed between 2 atoms by sharing electrons.Carbon atom has 4 electrons so it can form a maximum of 4 covalent bonds.*CarbonCarbon Single BondsC has ability to share electrons not only with different elements but also with other carbon atoms.In this case the electrons are shared equally between the two identical carbon atomsAs shown below in the example two C atoms may be bonded to one another, and each of these carbon atoms may be linked to other atoms (Chains).**Polar Covalent BondsA polar covalent bond is a covalent bond in which the electron pair is not shared equally between the two atoms.Example: Hydrogen chloride molecule (HCl)In case of HCl, the shared electron pair is attracted more toward the chlorine, which therefore is slightly negative (partial negative charge) with respect to the hydrogen.**Multiple Covalent BondsIn a double bond, two electron pairs are shared between two atoms.Nonbonding electrons, or unshared electron pairs, reside on one atom.In a triple bond , three electron pairs are shared between two atoms.*Hydrocarbons are compounds composed of just hydrogen and carbon atoms.*ValenceThe valence of an element is the number of bonds that an atom of the element can form.The number is usually equal to the number of electrons needed to fill the valence shell.Oxygen, for example, has six valence electrons but a valence of only 2.*IsomerismThe molecular formula of a substance gives the number of different atoms present.The structural formula indicates how those atoms are arranged. Isomers are molecules with the same number and kinds of atoms but different arrangements of the atoms. *Structural (or constitutional ) isomers have the same molecular formula but different structural formulas.*Writing Structural FormulasIn a continuous chain, atoms are bonded one after another.In a branched chain , some atoms form branches from the longest continuous chain.*Abbreviated Structural FormulasIn a continuous chain, atoms are bonded one after another.In a branched chain , some atoms form branches from the longest continuous chain.*Line segment structureClassification According to Molecular FrameworkThe three main classes of molecular frameworks for organic structures are acyclic, carbocyclic, and heterocyclic compounds.Acyclic compounds contain no rings. Carbocyclic compounds contain rings of carbon atoms. Heterocyclic compounds have rings containing at least one atom that is not carbon.**Acyclic compounds *Carbocyclic compounds *Heterocyclic compoundsAllotropic Forms of CarbonsThree forms are know:Graphite: soft, dark black solid with good electrical conduction.Diamond: formed over long geologic time periods, when graphite is subjected to extreme underground pressures. Diamond is clear, and is the hardest natural substance known.Fullerenes: the most common being C60 have shapes similar to soccer balls*Classification According to Functional GroupFunctional groups are groups of atoms that have characteristic chemical properties regardless of the molecular framework to which they are attached.*Classification According to Functional GroupFunctional groups are groups of atoms that have characteristic chemical properties regardless of the molecular framework to which they are attached.*****
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