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Chapter 2

Chapter 2. Families of Carbon Compounds. Basic Definitions. Hydrocarbons- Compounds containing only carbon and hydrogen. Alkanes- hydrocarbons that contain only carbon-carbon single bonds Alkenes- hydrocarbons that contain at least one carbon-carbon double bond

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Chapter 2

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  1. Chapter 2 Families of Carbon Compounds

  2. Basic Definitions • Hydrocarbons- Compounds containing only carbon and hydrogen. • Alkanes- hydrocarbons that contain only carbon-carbon single bonds • Alkenes- hydrocarbons that contain at least one carbon-carbon double bond • Alkynes- hydrocarbons that contain at least one carbon-carbon triple bond

  3. Basic Definitions, cont • Saturated hydrocarbons- hydrocarbons that contain no multiple bonds • Unsaturated hydrocarbons- hydrocarbons that contain multiple bonds such as double or triple bonds

  4. Aromatic Hydrocarbons • Aromatic Hydrocarbons- unsaturated, cyclic hydrocarbons. • Benzene is the simplest example • All the bonds of a benzene ring are the same lengths!! • All the carbons are sp2 hybridized • One lobe of each p orbital extends above the ring while the other extends below the ring

  5. Polar Covalent Bonds • Heteroatoms- atoms that form covalent bonds and have unshared pairs of electrons. • Ex. • When atoms of different electronegativity form covalent bonds, the electrons are not shared equally • The result is a Polar Covalent Bond

  6. Dipoles • As a result of the unequal sharing of electrons, a dipole is created. • Ex. • Dipoles and Dipole moments are important physical properties.

  7. Polar Bonds vs Polar Molecules • Any diatomic molecule in which the two atoms have different electronegativity will have a dipole moment • However, just because compounds have polar covalent bonds doesn’t mean they have dipole moments. • In order for a molecule to be polar, the center of partial positive charge and the center of partial negative charge must be in different locations.

  8. Polar Molecules, cont • Lone pairs will contribute more than electronegative elements • Ex. Water Ammonia • Dipole Moments in Alkenes account for the cis/trans isomers having different properties

  9. Functional Groups • Functional Groups are: • The part of the molecule where most reactions occur • The part of the molecule that most determines the chemical and physical properties of a compound • The basis by which compounds are grouped into families • The basis for the nomenclature system

  10. Alkyl Groups & the symbol R • Alkyl group- the groups we identify for the purpose of naming. They are obtained by removing a hydrogen from an Alkane. • Ex. • The symbol –R is used to generically represent an alkyl group.

  11. The Phenyl Group • Same concept as an Alkyl group, except the hydrogen is taken off a benzene ring • There are multiple abbreviations and symbols:

  12. Alkyl Halides • A compound in which a Halogen replaces one or more of the hydrogens on an Alkane. • These are also termed haloalkanes. • They are classified as primary, secondary, and tertiary based of the carbon the halogen is directly bonded to.

  13. Alcohols • Functional group is –OH attached to a sp3 carbon • They can be viewed as a hydroxyl derivative of an alkane or an alkyl derivative of water • They are also classified as 1o, 2o, and 3o

  14. Ethers • General Formula R-O-R or R-O-R’ • Derivatives of water where both hydrogens are replaced with alkyl groups • Usually named by naming alkyl groups and adding the word ether. • Use di-alkyl if alkyl groups are the same

  15. Amines • Organic derivatives of ammonia • Also classified as 1o, 2o, and 3obut by different criteria! • Amines are classified based on the number of carbons directly bonded to the Nitrogen. • The nitrogen is considered to be sp3 hybridized with the lone pair in a hybridized orbital.

  16. Aldehydes and Ketones • Both contain the carbonyl group • Aldehydes have at least one hydrogen bonded to the carbonyl carbon • Ketones have two carbons bonded to the carbonyl carbon. • General Formulas: • Examples:

  17. Carboxylic Acids • General Formula: • Functional groups is the carboxyl group • Examples

  18. Esters • General Formula • Widely used in flavors and scents.

  19. Amides • General Formula: • Examples

  20. Nitriles • General Formula: • Both carbon and nitrogen are sp hybridized • Usually named by adding the suffix nitrile to the end of the hydrocarbon name • Examples:

  21. Physical Properties and Structure • Melting Point and boiling point are easily measured physical properties. • They are used to identify and isolate organic compounds • When new substances are made, we have to make reasonably accurate estimates. • These estimates are based on the structure and the forces that act between molecules and ions

  22. Physical Properties and Structure, cont • The temperature at which phase changes occur are an indication of the strength of these intermolecular forces. • Melting Point- the temperature at which equilibrium exist between the well-ordered crystalline state and the more random liquid state

  23. Intermolecular Forces • Ion-Ion forces- electrostatic attractions between oppositely charged ions. • These forces are so strong that salts typically decompose before boiling. • Dipole-Dipole Forces- the attraction between the positive end of one polar molecule and the negative end of another polar molecule.

  24. Intermolecular Forces • Hydrogen Bonding- very strong dipole-dipole attractions that occur between a hydrogen atom bonded to small, strongly electronegative atoms (O, N, and F) and the lone pair of electrons on another such atom • Hydrogen Bonds are weaker than a covalent bond but much stronger then a regular dipole-dipole interaction

  25. Intermolecular Forces • van der Waals/London/Dispersion Forces- the intermolecular attraction that exists for all molecules that arise due to the spontaneous, uneven distribution of electrons in a covalent bond.

  26. Polarizability • Polarizability- the ability of the electrons to respond to a changing electronic field • Depends on how tightly or loosely electrons are held F < Cl < Br < I

  27. Boiling Point • Boiling Point- the temperature at which the vapor pressure of a liquid equals the pressure of the atmosphere above it. • Boiling Points are pressure dependant • Read section 2.13c Boiling Points, about BP’s and factors that affect BP’s

  28. Solubility • “Like dissolves Like” • Dissolving something is a lot like melting it • Ex. With organic compounds, you have to consider the predominant functionality

  29. Infrared Spectroscopy, IR • Useful, quick way to identify what functional groups are present • It is considered to be a fingerprint for organic compounds, in some instances • Have to be careful, it is a Qualitative technique, not a Quantitative.

  30. Infrared Spectroscopy, IR • It uses a wide range of frequencies in the infrared region • Covalent bonds absorb certain frequencies • From this absorption, we know what bonds are present • Results are graphed as absorption vs frequency

  31. Infrared Spectroscopy, IR • The frequency is often in wavenumbers, which is 1/λ (λ= wavelength) • Absorption is found by subtracting what passed through the sample from what was there when sample was no present • Covalent bonds are like springs and begin to vibrate when specific energies are absorbed.

  32. Types of Vibrations • Symmetrical Stretching • Asymmetric Stretching • In Plane Bending • Out of Plane Bending

  33. Infrared Spectroscopy, IR • There are different vibrational energy levels • When a bond absorbs a specific wavelength of IR, it becomes excited and moves from one energy level to another. • The frequency of a stretching vibration can be related to two factors: • The masses of the bonded atoms • The relative stiffness of the bond

  34. Infrared Spectroscopy, IR • Not all bonds are seen in IR • To be seen by IR, the dipole moment of a bond must change during vibration • General rule, symmetrical bonds do not show stretching peaks.

  35. Absorptions • Table 2.6, page 89

  36. Two types of IR problems • Predict spectrum from structure • Using Molecular Formula and Spectra, predict the structure

  37. Spectrum from Structure • List all bond types • List frequency ranges • Draw spectrum • Label peaks

  38. Using Molecular Formula and spectra to get structure • Calculate Double Bond Equivalents (DBE’s) • Draw possible structures • Identify major peaks in spectrum and match to possible structures

  39. Helpful suggestions: • Check region around 3000 • Is there a strong, broad peak around 3500 • Is there a sharp peak in range of 1630-1780

  40. Review Applications of Basic Principles, page 97

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