1 / 45

Chem 1152: Ch. 11

Chem 1152: Ch. 11. Organic Compounds: Alkanes. Organic Chemistry. What is it? Chemistry associated with carbon compounds Why do we care? Forms the basis of all life on earth Organic compounds include: Sugars that build nucleic acids Amino acids Biorganic compounds Drugs.

bao
Download Presentation

Chem 1152: Ch. 11

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chem 1152: Ch. 11 Organic Compounds: Alkanes

  2. Organic Chemistry What is it? • Chemistry associated with carbon compounds Why do we care? • Forms the basis of all life on earth • Organic compounds include: • Sugars that build nucleic acids • Amino acids • Biorganic compounds • Drugs

  3. Organic vs. Inorganic Compounds • Estimated 9 x 106 organic vs. 5 x 105 inorganic cmpds (18:1) • Organic compounds form mostly covalent bonds, while inorganic compounds are more polarized and ionic Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  4. Organic vs. Inorganic Compounds: Bonding Ionic 1- 1+ + Na Na Cl Cl EN: 0.9 EN: 3.0 Covalent H + H 4H C C H H EN: 2.1 EN: 2.5 • Both types can follow the octet rule

  5. EN and Atomic/Ionic Radius Na Cl Na Cl 2.23 Å 0.97 Å EN: 0.9 EN: 3.0 C C H H 0.79 Å 0.91 Å EN: 2.1 EN: 2.5 • As radius gets bigger, electrons are farther away from pull of nucleus, so EN gets smaller

  6. Atom radius gets bigger EN gets small

  7. Abundance of Organic Compounds • Why are there so many more organic compounds than inorganic? • Carbon has unique bonding characteristics • Strong, covalent bonds with C and H • Isomerism • Groups of carbon atoms can form more than one unique compound

  8. Why do atoms fill orbitals the way they do? Aufbau Principle Electrons fill orbitals starting at the lowest available (possible) energy states before filling higher states (e.g. 1s before 2s). Sometimes a low energy subshell has lower energy than upper subshell of preceding shell (e.g., 4s fills before 3d). Pauli exclusion principle QM principle that no two identical fermions (particles with half-integer spin) may occupy the same quantum state simultaneously (why paired electrons have different spin). Hund's rule Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. 2p 2s Energy 1s

  9. Electron pairs form bonds in valence shell 2p 3p 2p 3s 3p 1s 2s 1s 2s 3s Na Cl 3p Atoms stabilized when outer shell filled with e-. In the formation of NaCl, Na “gives” an e- to Cl to form ionic bond between elements. This results in ions Na+ having a filled second shell and Cl- having a filled third shell (2 e- in 3s and 6 e- in 3p.

  10. Bonding Characteristics of Carbon C 2p Valence shell electrons Energy 2s 1s

  11. Shells, Subshells, Orbitals • The number of subshells in a shell = shell number • The first subshell s has 1 orbital. Each successive subshell adds 2 more orbitals (1, 3, 5, 7, etc). • Each orbital can hold only 2 electrons of opposite spin. • An atom with n = 3 also includes all subshells and orbitals for n < 3: • 1s, 2s, 2p, 3s, 3p, 3d

  12. Bonding Characteristics of Carbon Q: If 2s electrons are already paired, with only 2 2p electrons unpaired, how does carbon form 4 covalent bonds? C 2p Valence shell electrons 2s 1s

  13. Orbital Hybridization Energy Tetrahedral geometry with bond angles = 109.5°

  14. Orbital Hybridization • An sp3orbital has a two-lobed shape, similar to the shape of a p orbital but with different-sized lobes. • Each carbon-hydrogen bond in methane arises from an overlap of a C (sp3) and an H (1s) orbital. • The sharing of two electrons in this overlap region creates a sigma (σ) bond. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  15. Carbon Bonding Characteristics • The four hybrid sp3 orbitals allow carbon to form four bonds. When carbon is joined to four substituents (i.e. CH4), the resultant configuration is tetrahedral in shape. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  16. Geometry and Bond Angles of Hydrocarbons Group Geometry Bond angles Examples Alkane Tetrahedral 109.5° 120° Trigonal Alkene Linear Alkyne 180°

  17. Classification of Hydrocarbons Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  18. Alkanes • Alkanes can be represented by the general formula CnH2n+2, where the n is the number of carbon atoms in the molecule. • More complex alkanes can be straight chained (normal) or branched. C | C — C — C | C branched alkane C — C — C — C — C normal alkane Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  19. Representing Organic Compounds

  20. Representing Organic Compounds Ex. 1

  21. Representing Organic Compounds Ex. 2

  22. Representing Organic Compounds Ex. 3

  23. Complexity of Organic Compounds • Organic compounds can consist of simple molecules like CH4 to very complicated molecules containing over a million carbon atoms. • Because of this, there are many ways C—C bonds can be arranged  isomerism Note: An “R” group can be anything. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  24. Isomerism Isomers: Compounds that have identical molecular formulas, but different arrangement of atoms. • Structural isomers:Same formula, different arrangement. • Stereoisomers: Same formula, same arrangement, different 3D orientation. Ex. Structural Isomers of C2H6O. At room temp: • Ethyl alcohol is a liquid, completely soluble in water. • Dimethyl ether is a gas, partially soluble in water. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  25. Isomerism • Structural isomers: Same formula, different arrangement.

  26. 3D Conformations of Alkanes • Molecules are not static, but in constant motion. • They, twist, turn, bend, vibrate, rotate around C-C bonds. • Rotation produces different conformations. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  27. Recognizing Isomers • Different conformations are not the same as structural isomers (butane, isobutene) • Two structures are STRUCTURAL ISOMERS only if bonds have to be broken and remade to convert one to the other.

  28. Functional Groups • Functional Groups:Unique reactive combination of atoms that differentiate organic compounds into classes. • Examples: • Except for alkanes, each functional group contains a multiple bond or at least one oxygen or nitrogen atom. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  29. Functional Groups Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  30. Functional Groups Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  31. Functional Groups Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  32. Functional Groups Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  33. Representing Organic Compounds

  34. Conformations of Alkanes • Which of the following pairs represent structural isomers, and which are simply the same compound? • Which are normal alkanes and which are branched alkanes? Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  35. Parent Alkanes • Name is prefix + ane. • Prefix designates the number of carbon atoms. • Alkyl groups: substituents (branches) on parent alkane. substituent parent

  36. Common Alkyl Groups

  37. Common Nonalkyl Groups Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  38. Naming Alkanes • Rules for naming alkanes have been standardized by IUPAC (International Union of Pure and Applied Chemistry) (Parent) (Substituents) substituent parent Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  39. Naming Alkanes • Find the longest continuous C chain. This is the Parent. • If 2 different chains of equal length are present, the parent is the one with the MOST branch points. • Number the atoms in the parent chain. • Begin numbering at the end nearest the 1st branch point. • If 1st point is the same at either end, begin at end nearest the 2nd, 3rd branch points. • We want to label this so that branch points are the lowest numbers possible. substituent parent Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  40. Naming Alkanes • Identify and number the substituents. • Assign a number to each substituent based on carbon number in parent chain. • Two substituents on the same carbon (not 3) get the same number. • If both substituents are the same, use the prefix di-. • If structure has multiple identical substituents, put them altogether in the name. For example: 2,3,4,5,6-pentamethyloctane. substituent parent Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  41. Naming Alkanes • Write name as a single word. • Separate prefixes with hyphens. • Use commas (no spaces) to separate numbers. • If 2 or more different substituents are present, cite in alphabetical order. • Multiplier prefixes (di-, tri-, tetra-, penta-, etc.) are NOT used for alphabetizing. • The prefixes sec- and t- are NOT used for alphabetizing, but iso- IS used for alphabetizing. substituent parent Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  42. Cycloalkanes Rules for naming cycloalkanes • Substituents are named so that the first one is determined alphabetically. • After the first one is identified, the others are numbered to get the lowest possible sequence of numbers. chloro-3-methylcyclopentane chloro-2,3-dimethylcyclopentane Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  43. Isomerism and cycloalkanes • Structural isomers: Same formula, different arrangement. • Stereoisomers: Same formula, same arrangement, different 3D orientation. • Geometric isomers: stereoisomers of cyclic atoms. • Rotation about C-C single bonds occurs in open-chain compounds but not within rings. • Cis-substituents on the same side. • Trans-substituents on the opposite side. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  44. General Physical Properties of Alkanes • C—C and C—H bonds are non-polar (similar EN) • Alkanes have lower MP and lower BP than other organic compounds • Odorless • Insoluble in water • Less dense than water • As the size of the alkane increases: • MP increases • BP increases • Density increases Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  45. Alkane Reactions • Alkanes are the least reactive of all organic compounds. • The most significant reaction of alkanes is combustion (rapid oxidation). • Many alkanes are used as fuels. • Methane – natural gas • Propane – used in gas grills • Butane – lighters • Gasoline – a mixture of hydrocarbons • CH4 + 2O2 CO2 + H2O • The CO2 produced by burning alkanes increases V and P of gasses. This is what pushes the pistons in a combustion engine.

More Related