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Lecture 10 : Organic Compounds

Lecture 10 : Organic Compounds. Spring 2014. Course lecturer : Jasmin Šutković 29 th April 201 4. Contents. International University of Sarajevo . Functional classes and types of Org. Compounds Alkanes Alkenes Alkynes Aromatic compounds Isomeric variations of Organic compounds

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Lecture 10 : Organic Compounds

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  1. Lecture 10:Organic Compounds Spring 2014 Course lecturer : Jasmin Šutković 29 th April 2014

  2. Contents International University of Sarajevo • Functional classes and types of Org. Compounds • Alkanes • Alkenes • Alkynes • Aromatic compounds • Isomeric variations of Organic compounds • Reactivity of Organic compound • Chemical reactions of Organic Compounds • Substitution • Addition • Elimination

  3. Functional Groups and Classes of Organic Compounds • Organic compounds are covalent compounds composed primarily of carbon and hydrogen • Carbon is unique among the elements in its ability to catenate, forming long chains and cyclic structures in a wide variety of compounds • Functional groupsare structural units that determine the chemical reactivity of a molecule under a given set of conditions – Can consist of a single atom or a group of atoms – Organic compounds are classified into several major categories based on the functional groups they contain

  4. Organic Compounds main classes

  5. Organic compounds functional groups

  6. ALKANES CnH2n+2 CH4 C2H6 C3H8 C4H10 etc. C2H6ethane H H H—C—C—H H H Single bond…

  7. sp3conformation • bond angles = 109.5o • σ-bonds (sigma) • Rotation about C--C (conformations)

  8. Two isomers of butane C4H10: CH3CH2CH2CH3n-butane CH3 CH3CHCH3isobutane Isomers are different compounds that have the same molecular formula

  9. Alkane name CH4 methane C2H6 ethane C3H8 propane C4H10 butanes C5H12 pentanes C6H14 hexanes C7H16heptanes C8H18 octanes C9H20nonanes C10H22decanes ……. C20H42eicosanes each new common name requires a new prefix…

  10. hexanes C6H14common names CH3 CH3CH2CH2CH2CH2CH3 CH3CHCH2CH2CH3 n-hexane isohexane

  11. IUPAC nomenclature (Geneva, 1920) NAMES OF RADICALS (ALKYL GROUPS): CH3- “methyl” CH3Cl methyl chloride CH3OH methyl alcohol, etc. CH3CH2- “ethyl” CH3CH2CH2- “n-propyl” CH3CHCH3“isopropyl” |

  12. IUPAC rules for naming alkanes: • parent chain = longest continuous carbon chain  “alkane”. • branches on the parent chain are named as “alkyl” groups. • number the parent chain starting from the end that gives you the lower number for the first branch (principle of lower number). • assign “locants” to the alkyl branches. • if an alkyl group appears more than once use prefixes: di, tri, tetra, penta…; each alkyl group must have a locant! • the name is written as one word with the parent name last. The names and locants for the alkyl branches are put in alphabetic order (ignore all prefixes except iso) separating numbers from numbers with commas and letters from numbers with hyphens.

  13. fossil fuels: natural gas petroleum coal petroleum is a complex mixture of hydrocarbons 1. solvents 2. fuels 3. raw materials for chemical syntheses separated into fractions by fractional distillation in an oil refinery

  14. AlkenesCnH2n “unsaturated” hydrocarbons C2H4 ethylene Functional group = carbon-carbon double bond sp2 hybridization => flat, 120o bond angles σ bond & π bond => H2C=CH2

  15. C3H6 propylene CH3CH=CH2 C4H8butylenes CH3CH2CH=CH2 α-butylene 1-butene CH3 CH3CH=CHCH3 CH3C=CH2 β-butylene isobutylene 2-butene 2-methylpropene

  16. There are two 2-butenes: cis-2-butenetrans-2-butene “geometric isomers” (diastereomers)

  17. CIS /TRANS or E-Z systems • E/Zsystem is now recommended by IUPAC for the designation of geometric isomerism. • Use the sequence rules to assign the higher priority * to the two groups attached to each vinyl carbon. • 2. * * * • * • (Z)- “zusammen” (E)- “entgegen” • together opposite

  18. Nomenclatureof alkenes (basic steps): • Parent chain = longest continuous carbon chain that contains the C=C. • alkane=> change –ane to –eneprefix a locant for the carbon-carbon double bond using the principle of lower number. • If a geometric isomer, use E/Z (or cis/trans) to indicate which isomer it is.

  19. * * (Z)-3-methyl-2-pentene (3-methyl-cis-2-pentene) * (E)-1-bromo-1-chloropropene *

  20. AlkynesCnH2n-2 C2H2H—C  C—H sp configuration Main representative is Acetylene OR Ethyne Example : C3H4CH3CCH propyneOR methyl-acetylene

  21. Nomenclature: • common names: “alkylacetylene” • IUPAC: parent chain = longest continuous carbon chain that contains the triple bond. • add -yne • prefix locant for the triple bond, etc. • CH3CH2CCCH32-pentyne • ethylmethylacetylene

  22. “terminal” alkynes have the triple bond at the end of the chain: CH3 CH3CH2CCH HCCCHCH2CH3 1-butyne 3-methyl-1-pentyne ethylacetylenesec-butylacetylene

  23. Aromatic compounds • Aromatic compounds are compounds which contain a benzene ring in their molecules • Benzene C6H6 • Methylbenzene C7H8 • EthylbenzeneC8H10

  24. Benzene The six carbon-carbon bonds in benzene are identical, intermediate in length between double and single bonds

  25. Sigma bonding in benzene Six carbon atoms joined to form a hexagonal planar ring. Each carbon has four valence electrons! One of these is used to form a bond with a hydrogen atom. Two other electrons are used to form sigma bonds with the carbon atoms on either side.

  26. Range and scope of aromatic chemistry Pharmaceutical compounds, e.g. Morphine Herbicides (Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants) Detergents (e.g. Sodium dodecylbenzenesulfonate- It is a major component of laundry detergent ) Dyes

  27. Aromatic compounds and cancer Some aromatic compounds are carcinogenic, e.g. Benzene However, not all aromatic compounds are carcinogenic; aspirin is an example

  28. Organic compounds groups : 1. First family is the hydrocarbons, which include alkanes, with the general molecular formula CnH2n+2 where n is an integer; alkenes represented by CnH2n; alkynes represented by CnH2n–2; and arenes (CnHn) 2. Second family is the halogen-substituted alkanes, alkenes, and arenes, which include the alkyl halides and aryl halides

  29. 3.Third family is the oxygen-containing organic compounds, which are divided into two main types: • Those that contain at least one C–O single bond, which include alcohols, phenols, and ethers • Those that contain a carbonyl group (> CO), which include aldehydes, ketones, and carboxylic acids 4. Fourth family is the carboxylic acid derivatives; these are compounds in which the H atom on the –CO2H functional group is replaced either by an alkyl group, producing an ester, or by an amine, forming an amide 5. Fifth family is the nitrogen-containing organic compounds; these include amines, nitriles (which have a CN triple bond) and nitro compounds (which contain the NO2 group)

  30. Isomeric Variations in Structure • Isomers are different compounds that have the same molecular formula • Three main types of isomers: 1. Conformational 2. Constitutional (structural) 3. Stereoisomers

  31. Conformational Isomers • The C–C single bonds in alkanes are formed by the overlap of an sp3 hybrid orbital on one carbon atom with an sp3 hybrid orbital on another carbon atom, forming a  bond (sigma) • Differences in three-dimensional structure resulting from rotation about a  bond are called differences inconformation, and each different arrangement is called a conformational isomer

  32. • Differences between the conformations are depicted in drawings called Newman projections – A Newman projection represents the view along a C–C bond axis, with the carbon that is in front shown as a point and the carbon that is bonded to it shown as a circle

  33. – In one extreme, the eclipsed conformation, the C–H bonds on adjacent carbon atoms are parallel and lie in the same plane – In the other extreme, the staggered conformation, the hydrogen atoms are positioned as far from one another as possible

  34. Conformational Isomers • Newman projections are useful for predicting the stability of conformational isomers – The eclipsed conformation is higher in energy than the staggered conformation because of electrostatic repulsions between hydrogen atoms – The staggered conformation is the most stable because electrostatic repulsion between the hydrogen atoms on adjacent carbons is minimized

  35. Newmans projections

  36. Constitutional (Structural) Isomers • Constitutional (structural) isomers differ in the connectivity of the atoms – The two alcohols, 1–propanol and 2–propanol, have the same molecular formula (C3H8O), but the position of the –OH group differs, which causes differences in their physical and chemical properties • In the conversion of one constitutional isomer to another, at least one bond must be broken and reformed at a different position in the molecule

  37. Propanol…

  38. Stereoisomers •Stereoisomers are molecules that have the same connectivity but whose component atoms have different orientations in space • Two types of stereoisomers: 1. Geometric isomersdiffer in the relative placement of substituents in a rigid molecule; members of an isomeric pair are eithercisor trans, with interconversion between the two forms requiring breaking and reforming one or more bonds; their structural differences causes them to have different physical and chemical properties and to exist as two distinct chemical compounds

  39. Stereoisomers 2. Optical isomersare molecules that are mirror images but cannot be superimposed on one another in any orientation • Optical isomers have identical physical properties, although their chemical properties may differ • Molecules that are nonsuperimposable mirror images of each other are said to be chiral; an achiral object is one that can be superimposed on its mirror image

  40. Stereoisomers

  41. Stereoisomers • Most organic molecules that are chiral have at least one carbon atom that is bonded to four different groups – This carbon is designated by an asterisk in structural drawings and is called a chiral center, chiral carbonatom, asymmetric carbon atom, stereogenic center, orstereocenter • A molecule and its non-superimposable mirror image are called enantiomers!

  42. Stereoisomers

  43. Stereoisomers • Interactions of enantiomers with other chiral molecules • In living organisms, every molecule with a stereocenter is found as a single enantiomer, not a mixture • At the molecular level, our bodies are chiral and interact differently with the individual enantiomers of a particular compound • Only one enantiomer of a chiral substance interacts with a particular receptor, initiating a response; the other enantiomer may not bind at all, or it may bind to another receptor, producing a different response

  44. Cis and Trans conformations

  45. Reactivity of Organic Molecules • The reactivity of a molecule is affected by the degree of substitution of the carbon bonded to a functional group; the carbon is designated as primary, secondary, or tertiary – Primary carbon is bonded to only one other carbon and a functional group – A secondary carbon is bonded to two other carbons and a functional group – A tertiary carbon is bonded to three other carbons and a functional group

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