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Slide 2 Physical Properties As it is true for all substances, each organic compound has certain physical and chemical properties. some of the important physical properties of organic compounds are: melting point, boiling point, density, and solubility Slide 3 Melting Point Melting point for an organic substance is the temperature at which it changes from solid state to liquid state. This temperature is also referred to as freezing point at which a compound changes its state from liquid to solid. Melting point determinations have importance in various applications. Such as: Making a comparison with the literature data to observe the same temperature. Having a very rough idea on the purity of a substance (there are much more available and accurate methods applied to decide it). Slide 4 To identify the melting point of a substance that is originally synthesized. some compounds have too low melting points, and some of them have very high melting points. There are lots of factors that affect the melting point. The chemical structure is the main determinant. In general; Melting points are higher for higher molecular weight compounds. Impurities decrease the melting point. ice-salt mixtures, Salt and soil, Ethylene glycol. Intramolecular and, in particular intermolecular forces, such as H-bonds, dipole dipole interactions increase the melting point. Slide 5 Loosing symmetry decreases the chance of intermolecular interactions. Solid state formation is deeply affected through the possibility of interaction among molecules. Therefore, loosing symmetry, in particular through branching lowers the melting point. Trans isomers are more stable than cis isomers, therefore they have higher melting points. Slide 6 Measuring the Melting Point Old Fashion Model Slide 7 New fashion model Slide 8 Boiling Point Boiling point for an organic substance is the temperature at which it changes from liquid state to gas (vapor) state. The vapor pressure of a liquid is also equal to the pressure of the current environment at its boiling point temperature. Unlike the melting point boiling point of an organic compound varies depending on the change at the environmental pressure. The lower atmospheric pressure---the lower the boiling point Slide 9 There are structural aspects having effect on boiling point: Higher molecular weight ---higher boiling point Intermolecular and intramolecular interaction Hydrogen bonding, Dipole-dipole interaction Vanderwals Increase boiling point Impurities Branching Slide 10 Density A density of a substance is calculated by dividing its weight to its volume. The unit generally employed for density is gr/mL (i.e., also referred to as gr/cm 3 ). pressure Temperature Polar groups Molecular weight Branching Double and triple bonds Slide 11 Measuring of density Pycnometers Slide 12 In this equation; W1= the weight of empty pycnometer W2= the weight of pycnometer filled with the sample liquid W3= the weight of pycnometer filled with the inert liquid. Measuring the density for liquid sample Slide 13 Measuring the density for solid sample In this equation; w 1 = the weight of pycnometer filled with the inert liquid. w 2 = the weight of empty pycnometer. w 3 = the weight of pycnometer added a little amount of solid sample. w 4 = the weight of inert liquid filled w 3. Slide 14 Solubility Solubility is the degree of dissolution of a substance in a solvent. The solubility of a liquid substance in another liquid matter --- miscibility and immiscibility, See table for solubility page 68 Slide 15 like dissolves like There are lots of interaction types that might take place in dissolution of a substance in a liquid. The organic molecules can not dissolve in water because; long carbon skeletons, absence of polar functional groups, absence of heteroatoms, absence of ionic structures, hydrophobic character Slide 16 Making salt (ammonium salt, carboxylic acid salt) These are typically prepared by employing acid base reactions (list of base and acid are in page 64,65) Make hydrogen bond (glucose, resorcinol) Having carboxylic, ketone-aldehyde, amine with 5 or less carbon atoms Like dissolves like, organic substances are soluble in organic solvent, but not all, varying depending on the structure of both the organic substance and the organic solvent, for instance; see, table of solubility of naproxen in page 70 Slide 17 Acetone has the ability of dissolve most of the organic molecules. For instance, the solubility of naproxen in acetone is 0.726 mol/L, which is quite higher than its solubility in other solvents. Utilizing the solubility data to estimate the presence of functional groups in an unknown molecules (see table in page 71) Slide 18 pH Henderson-Hasselbach equation: pH = pKa + log ([A - ] / [HA]) pH=pka---the concentration of ionized and non-ionized forms are equal pH>pKa---the concentration of ionized >non-ionized forms pH