1. Hydrocarbons and Nomenclature of organic compounds Mir Ishruna Muniyat

2. Organic Chemistry and Hydrocarbons Over a million organic compounds, with a dazzling array of properties Why so many?

3. Answer: Carbon’s unique bonding ability! Let’s start with the simplest of the organic compounds. These are the Hydrocarbons.

4. Organic Chemistry and Hydrocarbons Hydrocarbons contain only two elements: 1) hydrogen, and 2) carbon – simplest hydrocarbons called “alkanes”, which contain only carbon to carbon single covalent bonds (C n H 2n+2 ) – methane (CH 4 ) with one carbon is the simplest alkane. It is the major component of natural gas.

5. Organic Chemistry and Hydrocarbons Carbon has 4 valence electrons, thus forms 4 covalent bonds – not only with other elements, but also forms bonds WITH ITSELF (nonpolar) Ethane (C 2 H 6 ) is the simplest alkane with a carbon to carbon bond

6. Organic Chemistry and Hydrocarbons One carbon atom can form a single covalent bond with four hydrogen atoms.

7. Organic Chemistry and Hydrocarbons Ball-and-stick modelSpace-filling model Formulas and Models for Methane and Ethane

8. Classification of Organic Compounds A.Depending on the source of the organic compounds- 1.Natural compounds- refer to those that are produced by plants or animals. 2.2. Synthetic Compounds- that are prepared by reaction of other compounds are referred to as "synthetic".

9. Continued… B. Depending on the number of molecules present in the compound 1. Monomers: small molecules which may be joined together in a repeating fashion to form more complex molecules called polymers. Example: Methane, ethane, acetylene etc. 2. Polymers: A polymer may be a natural or synthetic macromolecule comprised of repeating units of a smaller molecule (monomers). Example: Polyethene.

10. C. Based on the presence of aromaticity, organic compounds can be classified into two groups: aliphatic and aromatic. 1. Aliphatic Compounds: They do not follow Huckel rule. Aliphatic compounds can be further classified in two ways: i) Based on the type of bond present in the structure, two types: a) Saturated (no double/triple bonds) and b) Unsaturated (double/triple bonds) ii. Based on the presence of rings / cycles, two types: a) Acyclic (Alkanes), b) Cyclic (Cycloalkanes).

11. C. Based on the presence of aromaticity, organic compounds can be classified into two groups: aliphatic and aromatic. Cyclic Aliphatic compounds can be further classified into two groups based on the presence of atoms in the ring: i) Alicyclic/Homocyclic: the ring or the cycle of the compound is made up only of carbon. Example: benzene, aniline, phenol etc. ii. Heterocyclic compound: one or more heteroatom (N, S, O, etc) may be present within the ring structure of the organic compound. Example: pyrrole, furan, thiophene, pyridine, quinoline, etc

12. C. Based on the presence of aromaticity, organic compounds can be classified into two groups: aliphatic and aromatic (Continued) 2. Aromatic compounds: Aromatic compounds are those, which follow Huckel's rule. They contain (4n + 2) number of delocalized pi- electrons. They have the general formula: CnH2n-6 [where n is equal to or greater than 6] D. Based on the number of functional groups present within the molecule, organic compounds can be classified into two groups: i) Mono functional: contain only one functional group and ii) Multifunctional compound: contain more than one functional group.

13. Straight-Chain Alkanes Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain pattern - meaning one linked to the next (not always straight) C-C-C C-C-C-C etc. Names of alkanes always will always end with –ane Combined with the -ane ending is a prefix for the number of carbons.

14. Alkanes Straight-Chain Alkanes Ethane is the simplest of the straight-chain alkanes, which contain any number of carbon atoms, one after the other, in a chain.

15. Straight-Chain Alkanes Homologous series- a group of compounds that have a constant increment of change In alkanes, it is: -CH 2 - (methylene)

16. Alkanes A group of compounds forms a homologous series if there is a constant increment of change in molecular structure from one compound in the series to the next.

17. Straight-Chain Alkanes Many alkanes used for fuels : methane, propane, butane, octane As the number of carbons increases, so does the boiling and melting pt. – The first 4 are gases; #5-15 are liquids; higher alkanes are solids Condensed structural formulas?

18. Alkanes

19. NOMENCLATURE Common system Examples 1. Give a name for the following compound Step #1, count the number of carbons and write down the memorized Latin name for that number (previous slide) Step #2, since this structure fits the alkane general formula, use the “ane” suffix propane Three carbon Latin root Alkane suffix

20. Latin Hydrocarbon Roots Number of Carbons Latin Root 1meth 2eth 3prop 4but 5pent 6hex 7hept 8oct 9non 10dec 11undec Latin Hydrocarbon Roots Number of Carbons Latin Root 12dodec 13tridec 14tetradec 15pentadec 16hexadec 17heptadec 18octadec 19nonadec 20eicos 21unicos 22doicos H H n-butane isobutane H C C C H H C H H C H H H H H H H Examples neopentane

21. NOMENCLATURE 1.Common system a.Works best for low molecular weight hydrocarbons b.Steps to give a hydrocarbon a common name: 1.Count the total number of carbon atoms in the molecule. 2.Use the Latin root from the following slide that corresponds to the number of carbon atoms followed by the suffix “ane”. 3.For unbranced hydrocarbons use the prefix normal, or n-, 4.Branched hydrocarbons use specific prefixes, as shown on a subsequent slide

22. 2. Systematic System of Nomenclature (IUPAC) Names recommended by IUPAC - the International Union of Pure and Applied Chemistry Find the longest continuous chain of carbon atoms. Use a Latin root corresponding to the number of carbons in the longest chain of carbons. Follow the root with the suffix of “ane” for alkanes Carbon atoms not included in the chain are named as substituents preceding the root name with Latin root followed by “yl” suffix. Number the carbons, starting closest to the first branch. Name the substituent's attached to the chain, using the carbon number as the locator in alphabetical order. Use di-, tri-, etc., for multiples of same substituent. If there are two possible chains with the same number of carbons, use the chain with the most substituents.

23. Substituent Names (Alkyl groups)

24. Alkanes A hydrocarbon substituent is called an alkyl group. An alkane with one or more alkyl groups is called a branched-chain alkane.

25. Naming Straight-Chain Alkanes IUPAC names may be long and cumbersome Common names may be easier or more familiar, but usually do not describe the chemical structure! – Methane is natural gas or swamp gas

26. Alkanes Branched-Chain Alkanes An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule is called a substituent.

27. Branched-Chain Alkanes Branched-chain means that other elements besides hydrogen may be attached to the carbon – halogens, oxygen, nitrogen, sulfur, and even other carbons – any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branched part

28. Branched-Chain Alkanes A hydrocarbon substituent is called an alkyl group or sometimes radicals – use the same prefixes to indicate the number of carbons, but -ane ending is now -yl such as: methyl, ethyl, propyl, etc. Gives much more variety to the organic compounds

29. Branched-Chain Alkanes Rules for naming – (go from right to left) - 1. Longest C-C chain is parent 2. Number so branches have lowest # 3. Give position number to branch 4. Prefix (di, tri) more than one branch 5. Alphabetize branches (not prefix) 6. Use proper punctuation ( - and, )

31. Branched-Chain Alkanes From the name, draw the structure, in a right-to-left manner: 1. Find the parent, with the -ane 2. Number carbons on parent 3. Identify substituent groups (give lowest number); attach 4. Add remaining hydrogens

32. - Page 700

33. Alkanes Draw 3-ethylpentane Draw 2,3,4-trimethylhexane

34. Section Quiz. 1. Choose the correct words for the spaces. Because carbon has ______ valence electrons, it can form ______________ bonds. a. four, four covalent b. four, four ionic c. six, six covalent d. six, four or fewer covalent

35. 22.1 Section Quiz. 2. Alkanes are hydrocarbons that contain only ___________ bonds. a. carbon-carbon b. single covalent c. carbon-hydrogen d. ionic

36. 22.1 Section Quiz 3. Choose the correct words for the spaces. Hydrocarbons are highly soluble in _______ solvents because they are ________ molecules. a. nonpolar, nonpolar b. nonpolar, polar c. polar, nonpolar d. polar, polar

37. Which one? Systematic Nomenclature continued.

38. Which one? Systematic Nomenclature continued. The one with the most number of substituent's

39. Which one? Systematic Nomenclature continued. The one with the least number of substituent's The top structure has four substituent's and the bottom has three substituent's.

40. Which one? Systematic Nomenclature continued. The one with the least number of substituent's The top structure has four substituent's and the bottom has three substituent's. Name = ?

41. Which one? Systematic Nomenclature continued. The one with the most number of substituent's The top structure has four substituent's and the bottom has three substituent's. Name = ? heptane

42. Which one? Systematic Nomenclature continued. The one with the least number of substituent's The top structure has four substituent's and the bottom has three substituent's. Name = 3,3,5-trimethyl-4-propylheptane

43. Another Example: Name = 3-ethyl-2,6-dimethylheptane

44. Another Example: Name = 3-ethyl-2,6-dimethylheptane Notice substituent's are in alphabetical order; di, tri, etc. do not participate in the alphabetical order

45. Line Structures A quicker way to write structures' (Condensed Structure) (A line structure of the above condensed structure) ethyl methyl

46. Complex Substituent's If the branch has a branch, number the carbons from the point of attachment. Name the branch off the branch using a locator number. Parentheses are used around the complex branch name. 1-methyl-3-(1,2-dimethylpropyl)cyclohexane 1 2 1 3

47. 47 More Examples: is 3-methyloctane, NOT 5-methyloctane Butan-2-ol 2-chlorobutane

48. Is 4,5-diethyl-2,2-dimethylheptane It is NOT 3,4-diethyl-6,6-dimethylheptane! Is 5-(1’-methylethyl)-2,2,4-trimethyloctane

49. 49 Substitution level and functional groups The ‘substitution level’ of a carbon atom in an organic compound is determined by the number of attached hydrogen atoms:

50. 50 Substitution level and functional groups continued… In the case of AMINES, the rules are also different: The rules differ for certain functional compounds e.g. alcohols:

51. Aromatic compounds: substitution position relative to group ‘X’ Substitution level and functional groups continued…

52. 52 Substitution level and functional groups continued… Functional groups will be dealt with as they arise, however the following should be committed to memory:

53. 53 Many common names persist in organic chemistry, despite IUPAC rules, e.g. Compound ‘Common’ nameIUPAC name AcetonePropanone FormaldehydeMethanal Acetic acidEthanoic acid DimethyletherMethoxymethane

54. Homologous Series Contain same elements and same functional group, Homolog can be represented by a general formula, Each homolog differ from one above and one below by a – CH 2 – unit, Series of compound can be prepared by similar methods, Homologs show similar chemical properties, They show a gradual variation in physical properties due to increase in molecular size and mass Examples: Alkanes (paraffins), alkenes (olefins), ethers, and alkynes (acetylenes)

55. Example of Homologous series

56. Electronegativity Power of that atom or functional group to attract electrons or electron density towards itself Depends on two factors- – Atomic number: magnitude/amount of positive charge on the nucleus – Atomic radius: distance between the valence electron and nucleus of an atom.

57. Electronegativity continued Atoms with higher atomic number and lower atomic radius have higher electronegativity.

58. Polarity of Bonds Electronegativity is responsible for showing polarity of bonds. The more electronegative atom drags the shared pair of electron towards itself Example: Hᵟ⁺– Fᵟ⁻ Polarity and reactivity: The higher the polarity, the higher would be the reactivity of the molecule Non-Polar molecules: between two atoms with same electronegativities Example: C – C, H – H, F – F

59. Classification of Reagents Electrophiles Nucleophiles Electrophiles: Electrophilic means electron-loving. They are- – electron-deficient – attack an electron-rich site in an organic molecule – represented by E+ – may be either be positively(+) charged or neutral molecules – Examples: H+, Cl+, Br+, I+, NO2+, CH3+, CH3CO+, C6H5N2+, BF3 etc.

60. Classification of reagents continued.. Nucleophiles: Nucleophilic means "nucleus loving" They are- – electron rich species – attracted to the positive nuclear charge of an electron poor species – attack the electron deficient site in an organic molecule – they may be either negatively (-) charged or neutral molecules – represented by Nu:- – Examples: Cl-, Br-, I-, OH-, NH3, R-NH2 etc.

61. Factors influencing organic reaction Organic reactions may or may not occur depending upon the density of electrons at the site of reaction in the substrate. Factors that influence electron density in the substrate are – Inductive effect Mesomeric effect Electromeric effect

62. 1. Inductive effect Refers to the polarity produced in a molecule as a result of higher electronegativity of one atom compared to another. It involves sigma (σ) electrons. It is denoted by placing an arrow head in the middle of the bond and direction of the arrow is towards the more electronegative atom. Two types- – Positive Inductive Effect – Negative Inductive Effect

64. 2. Mesomeric effect Refers to the polarity produced in a molecule as a result of interaction between two π bond or a π bond and lone pair of electrons. It involves pi (π) electrons. It is denoted by a curved arrow and the direction of arrow indicates the movement of a pair of π- electron. This effect is more prominent in case of conjugated compounds. Two types- – Positive Mesomeric Effect – Negative Mesomeric effect

65. a) Positive mesomeric effect Atom/group -lose electron towards carbon are said to have + ve mesomeric effect. Ex: Cl. Br, I, OH, OCH3, NH2, NR2, NHR etc.

66. b) Negative Mesomeric effect Atom/group –draws electron from carbon are said to have -ve mesomeric effect. Eg: NO2. CN, CO etc

67. 3. Electromeric effect Refers to the polarity produced in a multiple bonded compound as it is approached by a reagent. It is also denoted by a curved arrow and involves π electrons. It is a temporary effect and occurs only in the presence of a reagent.

68. When a double/triple bond is exposed to an attack by an electrophile E+, the π electrons which form the π bond are completely transferred to one atom or the other.

69. Some definitions Melting point: The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point, the solid and liquid phases exist in equilibrium. Boiling point: The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into vapor. Ex: Ethanol (78.5°C) is a liquid at RT, Diethyl ether (-23.6°C) is a gas at RT. Solubility: It is the property of a solid, liquid, or gaseous chemical substances called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure of the surrounding environment.