Organic Chemistry Lecture Notes PDF

 Organic Chemistry 2  What is mean by organic chemistry? Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon- containing compounds. Most organic compounds contain carbon and hydrogen, but they may also include any number of other...

 Organic Chemistry 2  What is mean by organic chemistry? Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon- containing compounds. Most organic compounds contain carbon and hydrogen, but they may also include any number of other elements (e.g., nitrogen, oxygen, halogens, phosphorus, silicon, sulfur). What do organic chemists do? Organic chemistry is a highly creative science that allows chemists to create and explore molecules and compounds. Study of properties includes both physical properties and chemical properties, as well as methods to evaluate chemical reactivity, with the aim to understand the behavior of the organic matter in its pure form Structure of the atom The atomic number of an atom equals the number of protons in its nucleus The mass number of an atom is the sum of its protons and neutrons. Isotopes have the same atomic number (i.e., the same number of protons), but different mass numbers because they have different numbers of neutrons.  The Distribution of Electrons in an Atom The electrons in an atom can be thought of as occupying a set of concentric shells that surround the nucleus. An important point to remember is that the closer the atomic orbital to the nucleus, the lower is its energy. 5  The first shell consists of only an s atomic orbital; the second shell consists of s and p atomic orbitals; the third shell consists of s, p, and d atomic orbitals.  Chemical Bonding In trying to explain why atoms form bonds, G. N. Lewis proposed that an atom is most stable if its outer shell is either FILLED or CONTAINS EIGHT ELECTRONS and it has no electrons of higher energy. 1- Ionic bonding The atom that loses electrons becomes a positive ion (cation), while The atom that gains the electrons becomes a negative ion (anion). The ionic bond results from the electrostatic attraction between these oppositely charged ions. 7  2- Covalent bond A covalent bond is produced by the SHARING of a pair of valence electrons between two atoms. Atoms achieve NOBLE gas configurations by sharing electrons. 8 The sharing one pair of electrons between atoms is called a single bond. Two atoms can share two pairs or even three pairs of electrons; these multiple bonds are called double bonds and triple bonds, respectively. 9 3- Polar Covalent Bond 10  Electronegativity (EN). Is the tendency of an atom to pull bonding electrons toward itself resulting in a polar distribution of charge. Electronegativity measures the ability of an atom to attract electrons it is a measure for reactivity. 11  4- Hydrogen bonding A hydrogen bond is the electrostatic attraction between polar molecules that occurs when a hydrogen (H) atom bond to a highly electronegative atom such as NITROGEN (N), OXYGEN (O) or FLUORINE (F) experiences attraction to some other nearby highly electronegative atom. The name HYDROGEN BOND is something of misleading, as it is not a true bond but a particularly strong dipole-dipole attraction, and should not be confused with a covalent bond. 12 Types of chemical reactions 1- Substitution reaction Is a chemical reaction during which one functional group or atom in a chemical compound is replaced by another functional group or another atom. Substitution reactions are of prime importance in org or another atomic chemistry. Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved  2- Addition Reactions Is a reaction in which atoms or groups are attached to the molecule without displacement of any other atoms or groups. Only unsaturated compounds give addition reaction. 3- Elimination Reactions Is a reaction in which atoms or groups are detached from the molecule without displacement of any other atoms or groups. This reaction is reverse of addition reaction 14  Types of Reagents 1) Nucleophiles or Nucleophilic reagents (Electron Donors) are nucleus loving reagents which in a reaction donate electrons to share by its with the center attached 15 A- Negatively charged anions as: OH-, CN-, RO- OH + R X R OH + X B- Neutral molecules having lone pair of electrons R3N: H3N: H2O: R2O: R2S : 16 2) Electrophiles or Electrophilic reagents (electron acceptors = electron loving reagents ) Positively charged cations Such as, H+, NO2+, CH3+ 17  organic compounds 18 19  Alkanes Alkanes are compounds of only CARBON and HYDROGEN atoms and contain only SINGLE BONDS. Compounds that contain only carbon and hydrogen are called HYDROCARBONS, so an alkane is a hydrocarbon that has only single bonds. Alkanes in which the carbons form a CONTINUOUS CHAIN with NO BRANCHES are called STRAIGHT-CHAIN ALKANES 20 Nomenclature of alkanes If you look at the relative numbers of carbon and hydrogen atoms in the alkanes listed in the following table, you will see that the general molecular formula for an alkane is CnH2n+2 where n is any integer. So, if an alkane has one carbon atom, it must have four hydrogen atoms; if it has two carbon atoms, it must have six hydrogens. We have seen that carbon forms four covalent bonds and hydrogen forms only one covalent bond. 21  No. of Structure Name carbons 1 CH4 Methane 2 CH3CH3 Ethane 3 CH3CH2CH3 Propane 4 CH3CH2CH2CH3 Butane 5 CH3CH2CH2CH2CH3 Pentane 6 CH3CH2CH2CH2CH2CH3 Hexane 7 CH3CH2CH2CH2CH2CH2CH3 Heptane 8 CH3CH2CH2CH2CH2CH2CH2CH3 Octane 9 CH3CH2CH2CH2CH2CH2CH2CH2CH3 Nonane 22 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 Decane Rules of nomenclature of alkanes 1. Determine the number of carbons in the longest continuous carbon chain. This chain is called the parent hydrocarbon. The longest continuous chain is not always a straight chain; sometimes you have to “turn a corner” to obtain the longest continuous chain. 2. The name of any alkyl substituent that hangs off the parent hydrocarbon is cited before the name of the parent hydrocarbon, together with a number to designate the carbon to which the alkyl substituent is attached. The chain is numbered in the direction that gives the substituent the lowest number. 3- If more than one substituent is attached to the parent hydrocarbon, the chain is numbered in the direction that will result in the lowest possible number in the name of the compound. The substituents are listed in alphabetical. If two or more substituents are the same, the prefixes “di,” “tri,” and “tetra”are used to indicate how many identical substituents the compound has CH3CH2CHCH2CHCH3 CH3 CH3 2,4-dimethylhexane 4- If a compound has two or more chains of the same length; the parent hydrocarbon is the chain with the greatest number of substituents CH3CH2CHCH2CH2CH3 H3CHC CH3 3-ethyl-2-methylhexane (two substituents)  Cycloalkanes Are alkanes that have carbon atoms that form a ring (called alicyclic compounds). They have a molecular formula of CnH2n and contain carbon atoms arranged in a RING. Simple cycloalkanes are named by adding the prefix CYCLO- to the name of the acyclic alkane having the same number of carbons. 27 Rules of nomenclatures 1- In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent hydrocarbon and there is no need to number the position of a single substituent on a ring. CH3 H3CH2C methylcyclopentane ethylcyclohexane 28 2- In the case that the substituent has more carbon atoms than the ring, the substituent will be the parent hydrocarbon and the ring is named as a substituent. 29 3- If the ring has two different substituents, they are cited in alphabetical order and the number 1 position is given to the substituent cited first. CH3 H3C CH2CH3 1-ethyl-2-methylcyclopentane CH3 1,3-dimethylcyclohexane 30 4- If there are more than two substituents on the ring, they are cited in alphabetical order. The substituent given the number 1 position is the one that results in a second substituent getting as low a number as possible. H3CH2CH2C H3C CH2CH3 4-ethyl-2-methyl-1-propylcyclohexane not 1-ethyl-3-methyl-4-propylcyclohexane because 2 < 3 not 5-ethyl-1-methyl-2-propylcyclohexane 31 because 4 < 5  Synthesis of Alkanes 1- Hydrogenation of Alkenes The double bond of an alkene consists of a sigma (σ) bond and a pi (π) bond. Because the carbon-carbon π bond is relatively weak, it is quite reactive and can be easily broken and reagents can be added to carbon. Reagents are added through the formation of single bonds to carbon in an addition reaction. 32 2- Hydrolysis of Grignard Reagent Grignard reagent is formed reaction of alkyl halides with Magnesium in dry solvent (diethyl ether). Hydrolysis of Grignard reagent with water gives the alkane. Mg H2O Br MgBr Et2O 33 Reactions of Alkanes Halogenation is the replacement of one or more of H atoms in an organic compound by a HALOGEN (such as FLUORINE, CHLORINE, BROMINE or IODINE). The halogenation of an alkane appears to be a simple substitution reaction in which a C-H bond is broken and a new C-X bond is formed. The chlorination of methane, shown below, provides a simple example of this reaction: CH4 + Cl2 + energy ——> CH3Cl + HCl 34 The following facts must be accommodated by any reasonable mechanism for the halogenation reaction 1.The reactivity of the halogens decreases in the following order: F2>Cl2>Br2>I2. 2.We shall confine our attention to CHLORINE and BROMINE, since FLUORINE is so explosively reactive it is difficult to control, and IODINE is generally unreactive. 3.Chlorination and bromination are normally exothermic reactions, however, energy input in the form of heat or light is necessary to initiate these halogenations. 4.If light is used to initiate halogenation, thousands of molecules react for each photon of the absorbed. 5.Halogenation reactions may be conducted in either the gaseous or liquid phase. 35 The mechanism is illustrated in the following chart including 3 steps: 1-Initiation step; 2-Propagation step; 3-Termination step 36