Organic Molecules & Functional Groups PDF

Chapter 3 Organic Molecules & Functional groups ©2020 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education....

Chapter 3 Organic Molecules & Functional groups ©2020 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. 1  Hydrocarbons Hydrocarbons contain only the elements carbon and hydrogen. They may be aliphatic (ex. alkanes, alkenes, alkynes) or aromatic. ©2020 McGraw-Hill Education. 2  carbon to carbon bonds Molecules with C-C bonds can be linear or branched Classification of carbons: 1o primary: a C bonded to another C atom 2o secondary: a C bonded to two C atoms 3o tertiary: a C bonded to three C atoms 4o quarternary: a C bonded to four C atoms 1o And they can also be cyclical ©2020 McGraw-Hill Education. 3  Aliphatic Hydrocarbons Aliphatic hydrocarbons Atoms are connected in straight chains, branched chains or non-aromatic rings Three subgroups. Alkanes have only C—C single bonds and no functional group in the molecule (…ane) Alkenes have a C—C double bond.(…ene) Alkynes have a C—C triple bond. (..yne) ©2020 McGraw-Hill Education. 4  Aromatic Hydrocarbons Aromatic hydrocarbons are cyclic, planar (flat) compounds that contain resonance bonds….add to greater stability The simplest aromatic hydrocarbon is benzene. ©2020 McGraw-Hill Education. 5  Functional Groups A functional group is an atom or a group of atoms with characteristic chemical and physical properties. Most organic molecules contain a carbon backbone C—C and C—H bonds to which functional groups are attached. Structural features of a functional group include: Heteroatoms—atoms other than carbon or hydrogen. Functional groups can be on aliphatic or aromatic compounds ©2020 McGraw-Hill Education. 6  Functional Groups Functional groups distinguish one organic molecule from another. geometry physical properties reactivity ©2020 McGraw-Hill Education. 7  Reactivity of Functional Groups Heteroatoms and bonds allow reactivity Heteroatoms lone pairs create electron-deficient sites on carbon. Polarity of bond can allow the bond to “break” Nucleophile: species that donates an electron pair (Lewis bases) Electrophile: electron pair acceptor (Lewis acid)(accepts into an empty orbital) ©2020 McGraw-Hill Education. 8  Parts of a Functional Group R is shorthand notation ©2020 McGraw-Hill Education. 9  Ethane, a Molecule with No Functional Group Ethane is an alkane only C—C and C—H bonds are present It contains no polar bonds, lone pairs, or bonds. no reactive sites (no functional groups). ethane and other alkanes are very unreactive. ©2020 McGraw-Hill Education. 10  Comparison of ethane & ethanol-1 example of what can functional group do….. Ethanol has OH group (called a hydroxy group) attached to its backbone..alcohol lone pairs and polar bonds…..reactivity H replaced by OH ©2020 McGraw-Hill Education. 11  Functional Groups with Carbon- Heteroatom ( − ) bonds Several types of functional groups contain C—Z bonds. Z represents an electronegative heteroatom polar bond, carbon becomes electron deficient. ©2020 McGraw-Hill Education. 12  Functional Groups with − bonds (start recognizing functional groups) ©2020 McGraw-Hill Education. 13  Functional Groups with = Group = “carbonyl group”. polar C—O bond: carbonyl carbon is an electrophile, O becomes a nucleophile and base because of the lone pairs. π (pi) bond that is more easily broken than a C—O б (sigma)bond. ©2020 McGraw-Hill Education. 14  Functional Groups with = Group-1 ©2020 McGraw-Hill Education. 15  Multi-functional molecule Don’t let the complexity of the molecule confuse you Look for the functional group of “interest” for chemical reaction points Vitamin B2 Image From: http://www.chm.bris.ac.uk/motm/vitaminB2/vitaminb2h.htm ©2020 McGraw-Hill Education. 16  Importance of Functional Groups A functional group determines all of the following properties of a molecule: bonding and shape type and strength of intermolecular forces physical properties nomenclature chemical reactivity ©2020 McGraw-Hill Education. 17  Intermolecular Forces Intermolecular forces are interactions that exist between molecules. Functional groups determine the type and strength of these interactions. Ionic and covalent compounds have very different intermolecular interactions. ©2020 McGraw-Hill Education. 18  Intermolecular Forces in Covalent Molecules Molecules make up covalent compounds Functional group(s) on the molecule determine the type of forces that are involved. van der Waals forces (weakest) dipole-dipole interactions hydrogen bonding (strongest) (remember to think of molecules in terms of having an electron cloud around them) ©2020 McGraw-Hill Education. 19  Dispersion Forces in Molecules dipoles Nonpolar molecules do not have a dipole dipole attraction (induced) From: Corwin; Introduction to Chemistry, 8th edition ; Chapter 11 ©2020 McGraw-Hill Education. 20  Dipole Forces Polar molecules have a permanent dipole. The oppositely charged ends of polar molecules are attracted to each other; this is the dipole force. From: Corwin; Introduction to Chemistry, 8th edition ; Chapter 11 ©2020 McGraw-Hill Education. 21  van der Waals Forces (London Forces) very weak interactions caused by momentary changes in electron density in a molecule..temporary dipoles. ©2020 McGraw-Hill Education. 22  Example: van der Waals Forces in Methane CH4 doesn’t have a net dipole. At any one instant its electron density may not be completely symmetrical, resulting in a temporary dipole. This can induce a temporary dipole in another molecule. ©2020 McGraw-Hill Education. 23  van der Waals Forces and Surface Area All compounds exhibit van der Waals forces. The larger the surface area of a molecule, then larger the attractive force between two molecules, and the stronger the intermolecular forces. Figure 3.1 ©2020 McGraw-Hill Education. 24  Dipole-Dipole Interactions Dipole-dipole interactions: attractive forces between the permanent dipoles of two polar molecules, stronger than van der waals molecules align so that the opposite partial charges are in close proximity. ©2020 McGraw-Hill Education. 25  Hydrogen Bonding Hydrogen bonding occurs when a hydrogen atom bonded to O, N, or F, is electrostatically attracted to a lone pair of electrons in another molecule containing one of those 3 atoms Hydrogen bonding is the strongest of the three types of intermolecular forces. ©2020 McGraw-Hill Education. 26  Intermolecular Forces—Summary As the polarity of an organic molecule increases, so does the strength of its intermolecular forces. Understanding these forces helps to understand behavior of molecules ©2020 McGraw-Hill Education. 27  Physical Properties—Boiling Point boiling point is the temperature at which liquid molecules are converted into gas. energy is needed to overcome the attractive forces in the more ordered liquid state. stronger the intermolecular forces, the higher the boiling point. For compounds with approximately the same molecular weight: ©2020 McGraw-Hill Education. 28  Boiling Point and Intermolecular Forces relative strength of the intermolecular forces increases from pentane to butanal to 1-butanol. boiling points of these compounds increase in the same order. mol. wt = 72 g/mol 76 g/mol 74 g/mol ©2020 McGraw-Hill Education. 29  Other Factors Affecting Boiling Points For compounds with similar functional groups, boiling point increases as: The surface area increases (more area “touch” between molecules) The polarizability of the atoms increases.(larger atoms are more polarizable) Figure 3.2 ©2020 McGraw-Hill Education. 30  Melting Point melting point: temperature at which a solid is converted to its liquid phase. In melting, energy is needed to overcome the attractive forces in the more ordered crystalline solid…stronger the intermolecular forces, the higher the melting point. The stronger the intermolecular attraction, the higher the melting points (the same is true for boiling points). ©2020 McGraw-Hill Education. 31  Melting Point Trends For covalent molecules of approximately the same molecular weight, the melting point depends upon the identity of the functional group. Given the same functional group, the more symmetrical the compound, the higher the melting point For compounds having the same functional group and similar molecular weights, the more compact and symmetrical the shape, the higher the melting point. ©2020 McGraw-Hill Education. 32  Problem 3.47 : example of how this works Explain why benzene has a lower B.P. but higher m.p. than toluene Benzene: bp: 80 oC; mp 5 oC Toluene: bp: 111 oC; mp -93 oC Boiling point: no functional groups; intermolecular forces are dominant feature: Benzene has less surface area than toluene and weaker van der waals interactions, so its bp is lower Melting point: benzene is more symmetrical than toluene, so its molecules can pack closer together in the solid….more energy is needed to melt it than toluene ©2020 McGraw-Hill Education. 33  Solubility (more trends/behavior of molecules) Solubility is the extent to which a compound (solute) dissolves in a liquid (solvent). interactions between the solute and the solvent provide the energy needed to break the solute-solute interactions…dissolution ©2020 McGraw-Hill Education. 34  Solubility Trends “Like dissolves like.” Polar compounds dissolve in polar solvents like water or alcohols capable of hydrogen bonding with the solute. Nonpolar or weakly polar compounds dissolve in: nonpolar solvents (e.g., carbon tetrachloride and hexane). weakly polar solvents (e.g., diethyl ether). ©2020 McGraw-Hill Education. 35  Solubility of Organic Molecules An organic compound is water soluble only if it contains one polar functional group capable of hydrogen bonding with the solvent for every five C atoms it contains.(generalization) For example, compare the solubility of butane and acetone in H2O and CCl4. ©2020 McGraw-Hill Education. 36  Butane and Acetone Solubility butane and acetone are both organic compounds, they are soluble in the organic solvent CCl4. Butane, nonpolar, is insoluble in H2O. Acetone is soluble in H2O, contains only three C atoms and O atom can hydrogen bond with an H atom of H2O. (new aspect of H- bonding..it can occur with an O that doesn’t have an attached H) ©2020 McGraw-Hill Education. 37  Water Solubility of Organic Molecules The size of an organic molecule with a polar functional group determines its water solubility. A low molecular weight alcohol like ethanol is water soluble. Cholesterol, with 27 carbon atoms and only one OH group, is too large for the OH group to solubilize by hydrogen bonding. ©2020 McGraw-Hill Education. 38  Hydrophobic and Hydrophilic The nonpolar part of a molecule that is not attracted to H2O is said to be hydrophobic.(water-hating) The polar part of a molecule that can hydrogen bond to H2O is said to be hydrophilic.(water loving) ©2020 McGraw-Hill Education. 39  Solubility Properties of Representative Compounds (look at trends) ©2020 McGraw-Hill Education. 40  Application—Vitamins This section of the textbook tries to show practical applications of the solubility “rules” summarized in table 3.5 Look at the molecules for practice Don’t be concerned with all the extra information that is given for each vitamin…simply apply the rules and predict the molecule’s solubility ©2020 McGraw-Hill Education. 41  Ex. Vitamin A Vitamin A is water insoluble because it contains only one OH group and 20 carbon atoms. ©2020 McGraw-Hill Education. 42  Ex. Vitamin C Each carbon atom is bonded to an oxygen which makes it capable of hydrogen bonding, and thus, water soluble. ©2020 McGraw-Hill Education. 43  Soap Structure Soap molecules have two distinct parts: There is a hydrophilic portion composed of ions called the polar head. There is a hydrophobic carbon chain of nonpolar C—C and C— H bonds, called the nonpolar tail. Figure 3.6 ©2020 McGraw-Hill Education. 44  Soap Structure For our purposes at this time: consider that soap appears to “dissolve” in water Example is a (fatty) carboxylic acid such as : R-CO2H That has been reacted to become a sodium salt Fatty acid is not water soluble But salt is…. organic molecules can have ionic bonded portions ©2020 McGraw-Hill Education. 45  Ionophores…molecules that complex cations Ex.Crown ethers are cyclic ethers containing several oxygen atoms that bind specific cations depending on the size of their cavity. Basic concept: Hydrophobic molecules can complex ions and allow them to pass or exist in a non-polar media until released when a polar media is reached….. ©2020 McGraw-Hill Education. 46  Functional Groups and Electrophiles All functional groups contain a heteroatom, a pi bond or both (electron density). Resulting in the formation of both electrophilic sites and nucleophilic sites Electron-rich sites (nucleophiles) react with electron poor sites (electrophiles). Carbon atom bonded to the heteroatom becomes slightly positive ©2020 McGraw-Hill Education. 47  Nucleophilic Sites in Molecules A lone pair on a heteroatom makes it basic and nucleophilic. π bonds create nucleophilic sites and are more easily broken than σ bonds. ©2020 McGraw-Hill Education. 48  Reaction of π Bonds with Electrophiles electrons are involved with reactions and electron density will move towards a positive charge +C C E Results in the addition of the electrophile to the double bond and generating another + charge ©2020 McGraw-Hill Education. 49  Reaction of Nucleophiles with Electrophiles Alkyl halides possess an electrophilic carbon atom, so they react with electron-rich nucleophiles. Key to these type of reactions is that the electrons move towards the less “electron rich” area….Nucleophile towards Electrophile ©2020 McGraw-Hill Education. 50  How do reactions occur based on electron density Determine if there is an electrophile and a nulceophile If so, then we can generally say that a reaction may occur :Nuc- E+ a, c, d) yes b, No both are nucleophiles ©2020 McGraw-Hill Education. 51  End Chapter 3 HW: Some home work problems are within the chapter. 3.12, 3.13, 3.15, 3.19, 3.20, 3.39, 3.50, 3.53, 3.57, 3.58 ©2020 McGraw-Hill Education. 52