organic introduction.pdf

1. INTRODUCTION A. History In 1807, Berzelius proposed that compounds derived from living things were organic and that all others were inorganic. The scientists then were certain that organic compounds could be produced only within living systems. Living things possess...

1. INTRODUCTION A. History In 1807, Berzelius proposed that compounds derived from living things were organic and that all others were inorganic. The scientists then were certain that organic compounds could be produced only within living systems. Living things possessed a vital force as a result of their origin. This belief came to be known as the Vital Force Theory. More than twenty years later in 1828, Friedrich Wöhler, a former student of Berzelius, was able to synthesize urea (H2NCONH2) using an inorganic material. Urea is an organic component of the urine of mammals. This event disproved the VF theory. The weight of evidence was against the Vital Force Theory and it became clear that the only distinguishing characteristic of organic compounds was the presence of the element carbon. Organic Chemistry, then refers to the study of the compounds of carbon. An immense diversity of compounds can be formed from the Carbon element, from the simple to the complex; such as methane, containing one carbon atom, to DNA, containing tens of billions of atoms. This is because of the carbon atoms’ unique ability for bonding, an extent not possible for atoms of any other element. Carbon atoms can form chains of thousands of atoms or rings of all sizes, which can form branches and cross links. Organic chemistry finds importance in various fields; from the chemistry of food, dyes, drugs, paper and inks, paints and plastics, gasoline and rubber tires, etc. It is fundamental to understanding biology and medicine. B. Organic vs. Inorganic Compounds Some compounds containing carbon, like carbon monoxide (CO), carbon dioxide (CO 2), carbonic acid (H2CO3), and polyatomic ions like bicarbonate (HCO3-), cyanide (CN-), cyanate (CNO-) and carbonate (CO32-) are considered inorganic substances because their properties resemble those of inorganic compounds. Table 1.1 Properties of Inorganic and Organic Compounds Inorganic Compounds Organic Compounds 1. High melting point and boiling point, 1. Low melting point and boiling point, low high densities. densities. 2. Generally soluble in water and rarely 2. Most are not soluble in water but are soluble in nonpolar solvents. generally soluble in nonpolar solvents 3. Conduct electric current(electrolyte) 3. Do not conduct current(nonelectrolyte) 4. Generally nonflammable 4. Generally flammable to produce CO2 5. Ionic bonding and water. 6. Reactions are fast since reactions 5. Covalent bonding between ions are fast. 6. Reactions are generally slower due to 7. Requires very high temperature to slower breakage of covalent bonds. decompose. 7. Decomposes easily when heated. C. Bond Polarity The uneven distributions of charges in covalent bonds result in a polar bond. Such is represented by a delta sign(δ); to indicate a small amount of positive charge (δ+) and a small amount of negative charge (δ-). The electronegativity values are used to predict if the bond is polar or nonpolar. Polar molecules are dipoles since a positive end and a negative end exist. Table 1.2 Predicting the Type of Bond Difference in Electronegativity Type of Bond Between Bonded Atoms 0.4 or less Nonpolar covalent 0.5 to 1.8 Polar Covalent 1.9 and greater Ionic Example: Classify these bonds as nonpolar covalent, polar covalent, or ionic. Difference in Electronegativity a. O-H Polar 3.5-2.1 = 1.4 b. N-H Polar 3.0-2.1 = 0.9 c. NaF Ionic 4.0-0.9 = 3.1 d. C-H Nonpolar 2.5-2.1 = 0.4 D. Intermolecular Forces Van der Waals Forces: The forces of interaction between molecules or intermolecular forces like London forces, Dipole-dipole forces and hydrogen bonding. Ion-Dipole Force exists between an ion and the partial charge on the end of a polar molecule. Positive ions are attracted to the negative end of a dipole, whereas negative ions are attracted to the positive end. Dipole-Dipole Force exists between neutral polar molecules. Polar molecules attract each other when the positive end of one molecule is near the negative end of another. London Dispersion Forces: Intermolecular forces resulting from attractions between induced dipoles. Fritz London, a German-American physicist recognized that the motion of electrons in an atom or molecule can create an instantaneous dipole moment. Dispersion forces tend to increase in strength with increasing molecular weight. Thus the boiling points of straight chain HC increase with increasing molecular weight. Hydrogen bonding is a special type of intermolecular attraction that exists between the hydrogen atom in a polar bond (particularly an H-F, H-O, or H-N bond) and an unshared electron pair on a nearby electronegative ion or atom (usually an F, O, or N atom in another molecule.)  Trend of Strength of the Intermolecular Forces London forces only < Dipole-dipole forces < Hydrogen bonding < Ion-dipole forces < Ionic bonding E. Functional Groups Because the compounds of carbon are so numerous, it is convenient to organize them into families that exhibit structural similarities. The simplest class of organic compounds is the hydrocarbons, compounds composed only of carbon and hydrogen. Other organic compounds containing other elements can be considered derivatives of hydrocarbons. The key structural feature of hydrocarbons, is the presence of stable carbon-carbon bonds. Carbon is the only element capable of forming stable, extended chains of atoms bonded through single, double, or triple bonds. Hydrocarbons can be divided into four general types, depending on the kinds of carbon-carbon bonds in their molecules; e. Alkanes f. Alkenes g. Alkynes h. Aromatic Hydrocarbons The members of these different classes of hydrocarbons exhibit different chemical behaviors but also have similarities; 1. Because carbon and hydrogen do not differ greatly in electronegativity (2.5 for carbon, 2.1 for hydrogen), hydrocarbon molecules are relatively nonpolar hence are almost completely insoluble in water , but they dissolve readily in other nonpolar solvents. 2. They tend to become less volatile with increasing molar mass because of London dispersion forces. Carbon combines with other atoms to form characteristic structural units called functional groups. Functional groups are important for three reasons. First, they are the units by which we divide organic compounds into classes. Second, they are the sites of chemical reaction; a particular functional group, in whatever compound it is found, undergoes the same types of chemical reactions. Third, functional groups serve as a basis for naming organic compounds. 1. Alcohols: has the characteristic structural feature of a carbon bonded to the –OH (hydroxyl) group. Ex. CH3CH2OH Ethanol 2. Aldehydes and Ketones contain a C=O (carbonyl) group. O O || || R─ C─H R ─ C ─ R’ Aldehyde Ketone  3. Carboxylic Acids have the characteristic structural feature of –CO2H (carboxyl; carbonyl + hydroxyl) group. The carboxyl group may be written in any of the following ways, all of which are equivalent. O || R─ C─OH RCOOH RCO2H Table 1.3 Some Functional Groups: Type of Compound Functional Group Simple Example When used as Name when used suffix as prefix Carboxylic Acid O O ║ ║ R —C—OH H3C—C—OH — oic acid Carboxy— Ethanal Carboxylic O O O O ║ ║ anhydrides ║ ║ H3C —C—O—C—CH3 —oic Anhydride —C —C—O—C—C— Acetyl Anhydride or Ethanoic Anhydride or Carboxylic Anhydride Carboxylic Esters O O ║ ║ H3C —C—O—CH3 Alkoxycarbonyl- —C —C—OR Methyl Ethanoate — oate Or Methyl Acetate Amides O O ║ ║ H3C —C—NH2 —amide Amido- R —C—NH2 Ethanamide or Acetamide Aldehydes O O ║ ║ R —C—H H3C —C—H —al Formyl- Ethanal or Acetaldehyde Ketones O O ║ ║ R —C—OH H3C —C—CH3 —one Oxo- Propanone or Acetone Alcohols R—OH CH3—OH Methanol —ol Hydroxy— Phenols Ar—OH —ol Hydroxy- │ OH Phenol Amines R—NH2 R—NH2 Amino-  Table 1.3................ (continued) Type of Compound Functional Group Simple Example When used as Name when used suffix as prefix Alkanes R—H CH3 (Methane) Contains only C-H CH3CH3 —ane Alkyl- and/or C-C single (Ethane) bonds Alkenes R R H H Alkenyl- \ / \ / C ═ C C ═ C / \ / \ —ane R R H H Ethene or Ethylene Alkynes R — C ═ C — R’ H— C═ C —H —yne Alkynyl- Ethyne or Acetylene Ethers R — O — R’ H3C — O — CH3 ether Alkoxy- Dimethyl Ether Halides R—X X=F,Cl,Br,I H3C — Cl None Chloro— Chloromethane Nitro O O ║ ║ R —N—O H3C —N—O None Nitro— Nitromethane F. Molecular and Structural Formulas Molecular formula shows the number of each type of atom that is present in the molecule of the compound. Ex. C2H6 Structural Formula shows the details of the bonding present in the molecule, i.e., which atoms are connected to which other atom.  Ex. H H H C C H H H Writing Structural Formulas 1. Full or Expanded Structural Formula: All the atoms and bonds are indicated. Ex. H H H C C H H H 2. Condensed Structural Formula: an abbreviated form of writing formulas. Shows no bonds Shows all carbon-carbon bonds but no carbon-hydrogen bonds. Ex. CH3CH3 3. Skeleton Structural Formula: shows only the carbon atoms in the molecule. 4. Line Structural Formula: uses lines to show the structure of the compound where; Carbon atoms are present at the intersection of two or more lines and wherever a line begins or ends. Hydrogen atoms bonded to Carbon are not shown. Because carbon always has a valence of four, we mentally supply the correct number of Hydrogens. All atoms other than carbon and hydrogen are shown. Ex.: G. ISOMERISM Isomers are compounds that have the same molecular formula but different structures. Although isomers are composed of the same collection of atoms, they differ in one or more physical or chemical properties such as color, solubility, or rate of reaction with some reagents. Structural Isomers (or Constitutional Isomer) are compounds that have the same molecular formula but different structures. Compounds that differ from each other in connectivity:  Ex. C4H10 CH3CHCH 3 CH3CH2CH2CH3 CH3 Butane Isobutane Ex. C5H10 CH2 H2C CH2 H2C CH2 CH3CH2CH2CH2CH3 Pentene Cyclopentane Stereoisomers have the same molecular formula, the same order of attachment of atoms in their molecules, but a different three-dimensional orientation of their atoms in space. Ex.: C4H8 H H H CH3 C C C C H3C CH3 H 3C H cis-2-Butene trans-2-Butene There are two groups of Stereoisomers; 1. Enantiomers- Stereoisomers that are nonsuperimposable mirror images 2,3,4-trihydroxybutanal (Erythrose) CHO OHC H C OH HO C H H C OH HO C H CH2OH HOH 2C 2. Diastereomers-Stereoisomers that are not mirror images. CHO CHO H C OH HO C H H C OH H C OH CH2OH HOH 2C Mirror image is the reflection of an object in a mirror. Chiral-from the greek “cheir” meaning hand; objects that are not superimposable on their mirror image. They show handedness.  Ex.: Your left hand and right hands are chiral. Achiral- an object that has no handedness; lacks chirality. Note: Enantiomers are different compounds hence have different physical properties one of which is their effect on the plane of polarized light. Polarimeter – a device for measuring the ability of a compound to rotate the plane of polarized light. Dextrorotatory- Rotation of the plane of polarized light to the right. Levorotatory- Rotation of the plane of polarized light to the left. H. THE IUPAC SYSTEM - (International Union of Pure and Applied Chemistry) - A General System of Nomenclature The name assigned to any compound with a chain of carbon atoms consist of three parts; a prefix, an infix )a modifying element inserted into a word), and a suffix. Each part provides specific information about the structural formula of the compounds. Prefix—Parent—Suffix 1. The prefix: tells what are and where are the substituents. a. Substituent prefixes - parts that identify what substituents are located on the main chain or ring. b. Locants – numbers that tell where substituents are located on the main chain or ring. 2. The parent part tells how many carbons and what and how many bonds are present. The infix (the modifying element inserted into the parent name)in the parent name tells what type of carbon-carbon bonds and how many of them are present in the parent chain Infix Nature of Carbon-Carbon Bonds in the Parent Chain. -an- All single bonds -en- One or more double bonds -yn- One or more triple bonds 3. The suffix tells the class of compounds to which the substance belongs. Suffix Class of Compound  -e Hydrocarbon -ol Alcohol -al Aldehyde -one Ketone -oic acid Carboxylic acid Ex.: Propene A hydrocarbon One carbon-carbon double bond Three carbon atoms Pentanoic Acid A carboxyl group Only carbon-carbon single bond Five carbon atoms