Chapter 1 Introduction to Organic Chemistry I PDF

College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Chapter 1: Introduction to Organic Chemistry I Chemistry Department CHEM 1450 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: Define Organic chemistry Illustrate factors that makes Carbon important Classify Hydrocarbons and Hydroca...

College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Chapter 1: Introduction to Organic Chemistry I Chemistry Department CHEM 1450 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: Define Organic chemistry Illustrate factors that makes Carbon important Classify Hydrocarbons and Hydrocarbons derivatives Distinguish the different formulas of organic compounds Define hybridization College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Study of carbon and its compounds Study of organic compounds. Study of hydrocarbon compounds and its derivatives TWO THINGS INVOLVED IN ORGCHEM 1. HYDROCARBON 2. HYDROCARBON DERIVATIVES College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ The building block of structural organic chemistry is the tetravalent carbon atom With few exceptions, carbon compounds can be formulated with four covalent bonds to each carbon, regardless of whether the combination is with carbon or some other element. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Molecules with carbon are ORGANIC. Carbon dioxide and molecules without carbon are INORGANIC. FACTORS WHY CARBON IS IMPORTANT 1. They are versatile. Can form up to four bonds (single, double, or triple) in rings or in chains 2. Bonds formed are high in energy. Ex. Diamond Functional groups in organic molecules o Are LESS stable than the carbon backbone but are more likely to participate in chemical reactions o Determine the characteristics and chemical reactivity of organic molecules. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon ONLY. 1. HYDROCARBON Aliphatic (R) Uncyclic / Open Structure Saturated No pi bond formation or all are single bonded Ex. Alkanes Aromatic (Ar) Factors to consider: 1. Should be cyclic (closed structure / no terminal Unsaturated point) Contain pi bonds 2. Planar (2D structure) / has double or 3. Has conjugated double triple bonds bond (alternating) Ex. Alkenes/Alkynes 4. Follows Huckel’s Rule #pi e- = 4n + 2 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ }If the organic compound does NOT follow the four general factors of an aromatic compound, then it’s aliphatic. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions. Order of priority MUST be observed College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A Lewis structure in which bonded electron pairs in covalent bonds are shown as lines. FYI: Kekulé was the first to suggest a sensible structure for benzene. He said The carbons are arranged in a hexagon, and he suggested alternating double and single bonds between them. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ To save space and time in the representation of organic structures, it is common practice to use "condensed formulas" in which the bonds are not shown explicitly. In using condensed formulas, normal atomic valences are understood throughout. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Sample: Acetone IUPAC Name: 2-propanone College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Also called the Line-Angle Formula It is represented in two dimensions, as on a page of paper. A skeletal formula shows the skeletal structure or skeleton of a molecule, which is composed of the skeletal atoms that make up the molecule. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ All atoms undergo hybridization red + white = pink… PURPOSE OF HYBRIDIZATIONs Form equivalent orbitals (orbitals with the same shape) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Chapter 2: Introduction to Organic Chemistry II Chemistry Department CHEM 1450 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: Define Forces among & inside molecules Illustrate the different types of bonds (intramolecular): o Metallic o Ionic o Covalent o Coordinate covalent Illustrate the different types of intermolecular forces College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Intermolecular Forces Are attractive forces between molecules } } Intramolecular Forces Are attractive forces hold atoms together inside a molecule College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Forces among & inside molecules } There are 2 types of attraction in molecules: intramolecular bonds & intermolecular forces } Intramolecular bonds (ionic, covalent (Polar and non-polar), coordinate, metallic) } Intermolecular forces (IMF) have to do with the attraction between molecules (versus intramolecular forces: the attraction between atoms in a molecule, metal, or compound) } The three IMFs are: 1) H-bonding, 2) dipole - dipole, and 3) London forces order of decreasing strength) (in College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Generally, intermolecular forces are much weaker than intramolecular forces College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Intramolecular Forces includes types of bonding inside the molecule:     Metallic Bond Coordinate Bond Ionic Bond Covalent Bond College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Metallic bonds are the forces of attraction between the free-floating valence electrons and the positively charged metal ions. These bonds hold metals together } College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Sodium chloride, or table salt, is an ionic compound consisting of sodium cations and chloride anions An ionic compound is a compound composed of cations and anions Ionic Bond: The electrostatic forces that hold ions together in ionic compounds, which are formed by the transfer of one or more electrons from one atom to another College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom Sodium and chlorine atoms combine in a one-to-one ratio, and both ions have stable octets Metal + Non-metal = Ionic Compound College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Mg Mg2+ + 2e- 2e- + 2 F Mg + 2F 2F - MgF2 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Covalent bond is a chemical bond in which two or more electrons are shared by two atoms } } } If the atoms share 2 electrons a single covalent bond is formed If the atoms share 4 electrons a double covalent bond is formed If the atoms share 6 electrons a triple covalent bond is formed College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Lewis structure of F 2 F F 7e- 7e- F F 8e- 8e- single covalent bond lone pairs lone pairs F F F F lone pairs lone pairs single covalent bond Lewis structure of water College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ H + O + H single covalent bonds H O H or H O H 2e- 8e- 2e- Double bond – two atoms share two pairs of electrons O C O or O O C double bonds 8e- 8e- 8e- double bonds Triple bond – two atoms share three pairs of electrons N N 8e- 8e- triple bond or N N triple bond 13 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } When two atoms bond their DIFFERENCE in electronegativity determines the covalent bond type Occurs between non metals Non Polar Covalent Bonds Polar Covalent Bonds Non Polar Covalent Bonds College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬  When electrons are shared equally  Has almost no electronegativity difference (0.0 to 0.4)  H-C Bond is non-polar, also any diatomic molecule with identical atoms is nonpolar (eg: O2, F2,N2) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Polar Covalent Bonds  Electrons are unequally shared  The greater the difference in electronegativity The more polar is the bond College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Describing Polar Covalent Bonds δ+ δ– H—Cl The plus sign shows that hydrogen has acquired a slightly positive charge. The minus sign shows that chlorine has a slightly negative charge.  The polar nature of the bond may also be represented by an arrow pointing to the more electronegative atom H—Cl College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Describing Polar Covalent Bonds College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Coordinate Bond A coordinate covalent bond, also known as a dative bond or coordinate bond is a kind of 2center, 2-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ions to ligands involves this kind of interaction. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Intermolecular Forces (IMF): (between molecules)  Hydrogen Bonding  Dipole-dipole interaction  London forces have seen that molecules can have a separation of charge } This happens in polar bonds (the College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } We + – H Cl greater the ΔEN, the greater the dipoles) Molecules are attracted to each other in a compound by these positive and negative forces + – + – College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } H-bonding is a special type of dipole dipole attraction that is very strong } It occurs when F, O, or N are bonded to H } They are given a special name (Hbonding) because compounds containing these forces are important in biological systems College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Non-polar molecules do not have dipoles like polar molecules. How, then, can non-polar compounds form solids or liquids? } London forces (also called van der Waal forces) are due to small dipoles that exist in non-polar molecules } Because electrons are moving around in atoms there will be instants when the charge around an atom is not symmetrical } The resulting tiny dipoles cause attractions between atoms/molecules (the greater the mass, the greater the London forces) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ London forces London forces Are present in all compounds Can occur between atoms or molecules Are transient in nature (dipole-dipole are more permanent). London forces are the weakest IMF. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } The bigger the IMF’s, the more energy it takes to overcome them...... thus ◦ The bigger the IMF’s, the higher the melting and boiling point } Bonds are stronger than IMF’s, so the melting and boiling points of covalent network solids (i.e.. diamond), ionic compounds (i.e.. salts), and metals (i.e.. iron) are much higher than molecular substances (i.e.. water) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Chapter 3: Introduction to Organic Chemistry III Chemistry Department CHEM 1450 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: } Explain the difference between the old and new concept of organic compounds } Explain why organic chemistry is named as the chemistry of carbon } Explain why a carbon atom forms four covalent bonds. } Illustrate the different forms of hydrocarbons and the saturation state of bonds } Identify two possible arrangements of carbon atoms in an alkane } Identify the IUPAK system in naming organic compounds } Explain the IUPAK rules in naming hydrocarbons College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } } } In the early days of chemistry, scientists classified chemical substances into 2 groups: Inorganic: those that were composed of minerals, such as rocks and nonliving matter Organic: those that were produced by living organisms, hence the name “organic” At the time, scientists believed that a “vital force”, only present in living organisms, was necessary to produce organic compounds. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } In 1828, German chemist Friedrick Wöhler disproved this theory by producing urea, an organic compound found in urine, from inorganic compounds NH4NCO → H2N-CO-NH2 (INORGANIC) (ORGANIC) } } Now organic chemistry is defined as the study of compounds containing carbon atom There are currently about 10 million organic compounds known to man College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } The simplest organic compounds are called hydrocarbons A hydrocarbon is an organic compound that contains only carbon and hydrogen College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ ◦ Recall that a carbon atom has four valence electrons and a hydrogen atom has one valence electron. So, one carbon atom can form a single covalent bond with four hydrogen atoms as shown: College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Because carbon has four valence electrons, a carbon atom always forms four covalent bonds. There is a carbon-carbon bond in ethane The ability of carbon to form stable carbon-carbon bonds is one reason that carbon can form so many different compounds College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ ◦ The electron pair in a carbon-hydrogen or a carboncarbon bond is shared almost equally by the nuclei of the atoms forming the bond. ◦ Thus, hydrocarbons are nonpolar molecules. ‘ The attractions between nonpolar molecules are weak van der Waals forces. ‘ So, hydrocarbons with low molar masses tend to be gases or liquids that boil at a low temperature. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Recall the general rule “like dissolves like.” ◦ A nonpolar compound and a polar compound will not form a solution. ◦ For example, because oil is a mixture of hydrocarbons, oil and water do not mix. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ ◦ Because a carbon atom forms four covalent bonds, it can bond not only to one or two other carbon atoms, but also to three or even four other carbons, resulting in branched chains. ◦ In organic chemistry, branches on a hydrocarbon chain are discussed as if they were substituted for a hydrogen atom on the chain. ‘ An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule is called a substituent. ‘ So, carbon atoms in a hydrocarbon can be arranged in a straight chain or in a chain that has branches College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } } } } } } } } } Methane,CH4 Ethane, CH3CH3 Propane, CH3CH2CH3 Butane, CH3CH2CH2CH3 Pentane, CH3CH2CH2CH2CH3 Hexane, CH3CH2CH2CH2CH2CH3 Heptane, CH3CH2CH2CH2CH2CH2CH3 Octane, CH3CH2CH2CH2CH2CH2CH2CH3 Nonane, CH3CH2CH2CH2CH2CH2CH2CH2CH3 Decane, CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Alkyl groups are named by removing the -ane ending from the parent hydrocarbon name and adding –yl Alkane – H = Alkyle gp College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Each carbon in an organic molecule can be categorized as a primary, secondary, tertiary, or quaternary carbon.  If the carbon atom has only one carbon attached to it, then the carbon is a primary carbon.  If two carbons are attached to the carbon atom, the carbon is a secondary carbon; if three carbons, a tertiary carbon; and if four carbons, a quaternary carbon. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Select the longest continuous chain of carbon atoms as the parent compound. } Number the carbon atoms in the parent carbon chain starting from the end closest to the first carbon atom that has an alkyl or other group. } Name the alkyl group and designate the position on the parent carbon chain by a number. } When the same alkyl group branch chain occurs more than once, indicate this repetition by a prefix (di-, tri-, tetra-, and so forth). } When several different alkyl groups are attached to the parent compound, list them in alphabetical order. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ 5 CH 3 4 CH 2 3 CH 2 2 CH CH3 pentane 1 CH 3 parent alkane College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ 5 CH3 4 CH2 3 CH2 2 CH CH3 1 C H3 alkyl group methylpentane College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ 55 CH3 44 CH2 33 CH2 22 CH 11 C H3 CH3 2-methylpentane College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ 5. Draw the structural formula for 2,2,4-trimethylpentane, or isooctane? College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Saturated Hydrocarbons “ALKANES” College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: } Identify alkanes and the several ways to express alkanes } Explain the bonding in alkanes according to VSEPR } Explain how hybridization occurs in carbon atom } Illustrate the formation of sigma bond in alkanes } Explain the physical properties of alkanes } Explain the chemical properties of alkanes } Illustrate the reactions of alkanes College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Alkane is a hydrocarbon in which there are only single covalent bonds With a general formula Can be acyclic (no rings) or cyclic (cycloalkanes) The simplest alkane is Methane (CH4), it is the major component of natural gas College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ There are several ways to draw the formulas for alkanes Kukle Skeletal College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } The table below shows the ball-andstick models, and space-filling models for methane and ethane Molecular Orbital Theory College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } Generate hybrid orbitals by “mixing” atomic orbitals in order to achieve the VSEPR geometries Based on the twin concepts that ◦ atoms are surrounded by regions of electron density ◦ regions of electron density repel each other College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ The Valence Shell Electron Pair Repulsion Model College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Two electron pairs in the valence orbital are arranged linearly } Three electron pairs are organized in a trigonal planar arrangement } Four electron pairs are organized in a tetrahedral arrangement College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ That’s why atomic orbitals undergo hybridization College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A tetrahedral atom has sp3 hybridization Head to head overlapping College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Intermolecular forces: College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } } } Van der Waals interactions (London dispersion forces)* These are instantaneous induced-dipole interactions Important interactions between nonpolar compounds Increases with the surface of interaction between molecules, and therefore increases with molecular weight Melting and boiling points: College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Melting and boiling points increase with increasing molecular weight within a homologous series College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Melting and boiling points: College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Solubility: Solubility – “Like dissolves like” Alkanes are nonpolar, hydrophobic They are soluble in nonpolar solvents and insoluble in water. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Solubility: College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Alkanes are rather unreactive due to the presence of only C—C and C—H bonds. Therefore, they make great nonpolar solvents. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } In addition to combustion reaction, Alkanes undergo two important reactions: } Halogenation } Dehydrogenation (Substitution) (Elimination) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Halogenation (Substitution Reaction): College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Dehydrogenation (Elimination Reaction): College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Summary College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Colors of Alkanes Summary }Methane to butane are colorless gases (propane and butane are easily condensed under pressure and are commonly sold as liquids) }Alkanes containing 5 carbons up to about 19 are colorless liquids (petrol and kerosene are mixtures of liquid alkanes, dye is added to the fluids for safety reasons) }Alkanes with more than about 20 carbon atoms are colorless, waxy solids (paraffin wax is a mixture of solid alkanes) College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Summary }Alkanes are less dense than water (alkanes float on top of water) }Alkanes are non-polar molecules so they are more soluble in non-polar solvents than they are in polar solvents. Alkanes are insoluble in water }The melting and boiling points of the shorter chain alkanes is low, but the melting and boiling of alkanes increase as the number of carbon atoms in the carbon chain increases College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Summary VOLATILITY Due to their low boiling points, lower alkanes are highly volatile. Volatility refers to the ability of a liquid to change into vapor state. Among alkanes volatility decreases with increase in chain length. Among isomeric alkanes more the branching, greater is the volatility At room temperature, alkanes from C1 to C4 are gases, from C5 to C16 they are liquids and higher alkanes are solids and wax like to some extent Summary College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } } } } Alkanes are relatively unreactive Alkanes do not react with strong acids, bases, oxidizing agents (oxidants) or reducing agents (reductants) 1. Alkanes combust (react rapidly with oxygen) releasing energy, which makes alkanes useful as fuels. 2.Alkanes will react with halogens such chlorine gas and bromine in the presence of ultraviolet light 3. Alkanes undergo elimination reactions to produce alkenes. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Un-Saturated Hydrocarbons “ALKENES & ALKYNES” College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ After this lecture, the student will be able to: } Describe the structural characteristics of alkenes. } Define the structural characteristics of alkynes } Explain the IUPAK system in naming alkenes & alkynes } Explain the hybridization in alkenes & alkynes } Identify the meaning of unsaturated organic compound } Identify some un-saturated compounds in our life College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ An organic compound that contains double or triple carbon-carbon bonds is called an unsaturated compound The ratio of the hydrogen atoms to carbon atoms is lower in an unsaturated compound than in a saturated compound College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ An alkene is a hydrocarbon that contains one or more carbon-carbon double covalent bonds, with formula At least one carbon-carbon bond in an alkene is a double covalent bond. Other bonds may be single carbon-carbon bonds and carbonhydrogen bonds. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } Ethene (C2H4) is the simplest alkene It is often called by the common name ethylene College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Find the longest carbon chain Enumerate the carbons such that the functional group, here the double bond, gets the lowest possible number Substituents are cited before the parent longest chain, along with a number indicating its position at the chain College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Trigonal planar geometry around each carbon atom The molecular orbitals of Ethene:   1s orbitals of the four hydrogen atoms 2s, 2px, 2py, and 2pz orbitals of the two carbon atoms Ethene College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A trigonal planar atom has sp2 hybridization College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A trigonal planar atom has sp2 hybridization College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Pi bond overlapping: side by side College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ A hydrocarbon that contains one or more carbon-carbon triple covalent bonds is called an alkyne At least one carbon-carbon bond in an alkyne is a triple covalent bond. Other bonds may be single or double carboncarbon bonds and carbon-hydrogen bonds. ◦ Like alkenes, alkynes are unsaturated compounds. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ } } } Alkynes are not plentiful in nature. The simplest alkyne is the gas ethyne (C2H2), which has the common name acetylene, and is shown at left. The triple bond restricts rotation in an ethyne molecule, which has a linear shape. College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ The method for naming alkynes is analogous to the naming of alkenes. However, the suffix is -yne rather than -ene. 4-methyl-2-pentyne College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ Ichthyothereol is a toxic polyyne compound found in the leaves and flowers of several plants in South and Central America fish poison,,,,,,,,,,,,,??????? College of Medicine – ‫ﻛﻠﯾﺔ اﻟطب‬ College of Medicine – ‫كلية الطب‬ ISOMERISM College of Medicine – ‫كلية الطب‬ After this lecture, the student will be able to: } Define isomerism } Illustrate the concept of isomerism in organic chemistry } Define isomers } Define constitutional (structural) isomers } Explain how the properties of constitutional isomers differ } Define stereoisomerism } Explain chiral & a chiral carbon atom } Identify two types of stereoisomers } Explain the cis/trans isomers } Explain the enantiomers College of Medicine – ‫كلية الطب‬ You may have noticed that the structures of some hydrocarbons differ only in the positions of substituents or of multiple bonds Even though both compounds have the formula C4H10, their boiling points and other properties differ Because their structures are different, they are different substances College of Medicine – ‫كلية الطب‬ } } } Isomerism Isomers are compounds that have the same molecular formula but different molecular structures The concept of isomerism illustrates the fundamental importance of molecular structure and shape in organic chemistry College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ Butane and 2-methylpropane represent a category of isomers called constitutional isomers, or structural isomers Constitutional isomers are compounds that have the same molecular formula but the atoms are joined together differently College of Medicine – ‫كلية الطب‬ Constitutional isomers differ in physical properties such as boiling point and melting point. They also have different chemical reactivity's In general, the more highly branched the hydrocarbon structure is, the lower the boiling point of the isomer will be compared with less branched isomers College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ Because molecules are three-dimensional structures, molecules with the same molecular formula and with atoms joined in exactly the same order may still be isomers Stereoisomers are molecules in which the atoms are joined in the same order but the positions of the atoms in space are different (with different spatial arrangement) Two types of stereoisomers are Diastereomers and Enantiomers College of Medicine – ‫كلية الطب‬ Cis-trans isomers, also known as geometric isomers, have atoms joined in the same order but the spatial orientation of the groups differs. The most common example of cis-trans isomerism occurs in molecules with double bonds. College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ Two arrangements are possible for the methyl groups and hydrogen atoms with respect to the rigid double bond in 2-butene. Cis configuration Trans configuration College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ CHIRALITY A molecule that is not identical to its mirror image is said to be chiral (kyral, from the Greek cheir, meaning “hand”). Stereocenters, or chirality centers: carbon atom bonded to four different groups College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ CHIRALITY College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ The second category of stereoisomerism occurs whenever a central atom has four different atoms or groups attached. Most commonly the central atom is carbon Pairs of molecules that are mirror images and not superimposable are called enantiomers, or optical isomers  These molecules are examples of enantiomers College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ College of Medicine – ‫كلية الطب‬ Unlike other isomers, enantiomers have identical physical properties such as boiling points and densities Enantiomers do, however, behave differently when they interact with other molecules that have asymmetric carbons Many molecules in your body have asymmetric carbons, so each enantiomer can have a different effect on the body College of Medicine – ‫كلية الطب‬ How do the physical and chemical properties of stereoisomers differ? College of Medicine – ‫كلية الطب‬ How do the physical and chemical properties of stereoisomers differ? Cis-trans isomers have different physical and chemical properties from each other. Enantiomers do not have different physical properties, but they do behave differently when they interact chemically with other molecules College of Medicine – ‫كلية الطب‬ BIG IDEA Hydrocarbons with the same molecular formula but different molecular structures can have different properties