CHEM219 / CHEM 219 Module 3: (Latest Update 2026 / 2027) Principles of Organic Chemistry with Lab | Questions & Answers | Grade A | 100% Correct – Portage Learning

CHEM219 / CHEM 219 Module 3: (Latest Update 2026 / 2027) Principles of Organic Chemistry with Lab | Questions & Answers | Grade A | 100% Correct – Portage Learning 2026 / 2027 Academic Year Q: Characterize each of the following objects as being chiral or achiral: a. Pencil b. Wine Glass c. Baseball Glove d. Orchestra Conductors' Baton e. Scissors Answer a. achiral b. achiral c. chiral d. achiral e. chiral Q: Draw each of the following structures on a piece of paper. Identify any stereo centers in each indication the carbon number corresponding to a stereo center. If there are no stereo centers in a compound state none a. 1,2-dimethycyclohexane b. 2,3,4-trimethylhexane c. 1-bromo-1,2-dichloropropane a. stereocenters at C1 and C2 Answer b. stereocenters at C3 and C4 Q: Question 2 part 2: 2,2 dichloropropane, 1,2 dichloroputane, 2 methylhexane Answer a. none b. one stereocenter at C2 c. one stereo center at C2 Q: Assign priority order (1-4; is greatest priority) to the following four groups for the purpose of deterring R and S configurations at a stereocenter Answer i. 3, 1, 2, 4 ii. 4, 3, 2, 1 Q: Based on the direction of twist of the following groups, assign an R or S orientation S orientation R orientation Answer R orientation Q: question 4 part 2 S orientation R orientation Answer S orientation Q: The Fischer projection formula of the molecule fructose is shown below. How many stereocenters are present in the fructose molecule? What is the maximum number of stereoisomers that could exist for this sugar? Answer a) 3 b) 8 stereoisomers Q: Question 5 part 2. Blood Sugar Answer a) 4 b) 16 Q: Assign an R/S configuration for the following chiral molecule . Explain Answer R configuration because this is a clockwise rotation Q: For each of the following molecules, determine if the C=C is in the E or Z configuration Answer a. E configuration b. Z configuration Q: Question 7 part 2 Answer a. Z configuration b. E configuration a. Which stereoisomers (if any) represents pairs of enantiomers? (list all the pairings that apply) Q: The molecule 2,3-dibromobutane has two stereocenters (C2 and C3) and thus can exist as a maximum of four different stereoisomers. The Fischer projections of these stereoisomers are shown below. Answer the questions which follow. b. Which stereoisomers (if any) represents pairs of diastereomers? ( list all the pairings that apply) c. Which stereoisomers (if any) represent a mess compound? Answer a.C/D are enantiomers b. the pairs of A/C, A/D, B/C, and B/D are diastereomers c. memo compound is A Q: Question 8 part 2 Answer a. a/c and b/d are enantiomers b. a/b, c/d, a/d, b/c are diastereomers c. a,b,c,d are meso compound Answer True Q: Determine if the statements below are true of false regarding pair of molecules shown. They have different boiling points Answer False Q: Determine if the statements below are true of false regarding pair of molecules shown. One rotates plane-polarized light in the opposite direction from the other Q: Determine if the statements below are true of false regarding pair of molecules shown. They have the same density Answer True Q: Determine if the statements below are true of false regarding pair of molecules shown. One rotates plane-polarized light by a different number of degrees than the other Answer False Q: Determine if the statements below are true of false regarding pair of molecules shown. They are non-superimposable mirror images of each other Answer True Q: Briefly explain why it is important for chemists, biologist, doctors and nurses to understand the principle of chirality in organic molecules. Answer It is important for people dealing in medicine because it is very important to know that chiral compounds can change greatly in their characteristics and if not administered carefully can lead to abnormalities. Q: Why is the concept of chirality an important topic to learn to learn in the study of organic chemistry? Answer Chirality is relevant to biology and can be seen in carbohydrates and amino acids. When humans consume drugs the different potencies and effects can be based on the chirality. So it is important to know all of the effects. Q: Assign R/S configuration Answer S configuration because it moves in a counter-clockwise way. Q: Assign priority Answer i) 2, 1, 3, 4 ii) 1, 2, 4, 3 Q: Draw each of the following and identify carbon number to stereo center Answer a) no stereocenter b) C3 stereocenter 3) C2 stereocenter Q: Stereochemistry Answer the study of the three-dimensional structure of molecules Q: Stereoisomers Answer Compounds with the same structural formula and connectivity but with a different 3D arrangement of the atoms in space. Q: Enantiomers Stereoisomers that that are non-superimposable mirror images. Enantiomers have the same connectivity but different orientations (twist) of the four atoms or groups in 3D space. Answer The two different forms of the chiral molecule (the "left-handed" form or a "right-handed" forms) How do the differences caused by steroisomers differ than the differences caused by constitutional isomers. Answer trans-stereoisomers have the substituents on opposite sides/faces of the ring or double bond While the structural differences between stereoisomers are more subtle than those between constitutional isomers, stereoisomerism is often responsible for significant differences in the chemical and physical properties of organic compounds, including the biochemical behavior of many compounds such as drug molecules, amino acids, carbohydrates, and nucleic acids. Several of the human senses, especially smell, are greatly affected by stereoisomerism in organic compounds. cis-stereoisomers have the substituents on the same side/face of the ring or double bond Chirality the concept of "handedness" in an object. Consider the difference between a pair of socks and a pair of gloves. A sock can be worn (interchangeably) on either the left or right foot, but the same is not true for the gloves. A left-handed glove cannot be worn on the right hand and vice-versa. The gloves possess the property of "handedness" (chirality) Observation will reveal that chiral objects are typically not symmetrical (asymmetric), while achiral objects typically exhibit multiple planes of symmetry within the object itself. chiral a molecule that is not superimposable on its mirror image (possesses the property of handedness) achiral A molecule that is superimposable on its mirror image (does not possess the property of handedness) What test can be applied to determine if an object is chiral or achiral? A simple test involves comparing the object and its mirror image for superimposability. Superimposability The ability to align (overlap) two objects so that every unique part of each is in direct alignment with the same unique part on the other. What does it mean when a molecule is a chiral molecule? An organic compound that can exist as two different forms ("left-handed" form or a "right handed" form) Is lactic acid structure chiral or achiral? Attempting to superimpose lactic acid and its mirror image reveals that the two forms cannot be superimposed, and thus, the molecule is chiral, and it exists as two separate forms known as enantiomers (Figure 3.4). No matter how one of the structures is rotated, it is impossible to get all of the atoms/groups in one to align with the same atoms/groups in the mirror image structure. Is the molecule 2-chloropropane chiral or achiral? When the 3D structure of this molecule is drawn, a tetrahedral geometry is observed around the central carbon, similar to that of lactic acid. At first glance, it may not be clear that the molecule is achiral. It is only through the application of the superimposability test that the molecule reveals its achiral nature. The absence of a stereocenter is the reason why molecules like 2-chloropropane are achiral. An analysis of the 3D structure of 2-chloropropane reveals a tetrahedral geometry around the central carbon but only three different types of atoms or groups attached (there were 4 bonds to the carbon but 2 of the groups were identical). The symmetrical nature of the 2 chloropropane molecule comes from having two of the same group on the central carbon - this allows the structure to be superimposed on its own mirror image, and thus, makes the molecule achiral. stereocenter A carbon atom with tetrahedral geometry that is bonded to four DIFFERENT atoms or groups (4 single bonds connected to four different atoms or groups). What is the most common cause of chirality in an organic molecule? The presence of a tetrahedral stereocenter. Identifying a stereocenter in an organic molecule is a way to quickly determine if an organic molecule may possess the property of chirality. This type of carbon is known as a stereocenter, a stereogenic center, or a chiral center. A chiral molecule will almost always possess one (or more) stereocenters. In contrast, most molecules without a stereocenter are not chiral. Stereocenter vs Chirality The stereocenter is the cause of the chirality, while chirality is a property of the molecule as a whole. What are two things that rule out a carbon from being a stereocenter? - if the carbon has more than one hydrogen on it (makes it so there can't be four different groups/atoms) - if the carbon has a double or triple bond (makes it so there cant be four separate bonds and therefore can't have tetrahedral geometry) How is the presence of a stereocenter in an organic structure is denoted? With an asterisk next to the stereogenic carbon Look at the image of 3-methylhexane and explain whether it has a stereocenter and why? Yes, it is chiral because it has a stereocenter. The substituents attached to carbon #3 are a methyl, an ethyl, a propyl, and a lone hydrogen (not pictured). While methyl, ethyl, and propyl are all carbon-based and very similar, they are not identical and that creates a stereocenter. Look up an image of 1-bromo-2-iodopropane and explain whether it has a stereocenter and why? Yes it does have a stereocenter. Only carbon #2 is a stereocenter because the #1 carbon that bears the bromine also bears two identical hydrogens (and thus is not a stereocenter). The presence of the bromine on carbon #1 makes this carbon different from the methyl group (carbon #3) and thus creates the stereocenter on carbon #2. Look at the image of cyclohex-2-ene-1-ol and explain whether it has a stereocenter and why? Yes it does have a stereo center on carbon #1. In the molecule cyclohex-2-ene-1-ol, stereocenters can exist in cyclic structures as well. The #1 carbon in this molecule is a stereocenter because there is a difference in connectivity (different groups) as we go counterclockwise vs clockwise around the ring from the number one carbon. How does the chirality of ibProfin impact the effects of the drug? When ibuprofen is synthesized, the two enantiomeric forms are produced in equal amounts, so you ingest both enantiomers. Only one of the enantiomeric forms is active at relieving pain and the other is inactive. The non-active enantiomer is slowly converted by enzymatic processes in the body to the active form, allowing for an fast and slow effects of the drug. How does the chirality of Thalidomide impact the effects of the drug? One of the enantiomers is therapeutic (treats nausea symptoms) and one of the enantiomers is toxic/has other harmful effects. Thalidomide was given to pregnant women in the late 1950's and early 1960's as a treatment for nausea. While one of the enantiomeric forms was active as a therapeutic, it was not known that the other form caused severe birth defects (teratogenic) in many of the children born to mothers who used the drug. Thalidomide was removed from the market for pregnant women shortly after this discovery. Many of the human senses are subject to the influence of chirality, which sense in particular is sensitive to chirality? Our sense of smell Describe the ways humans can sense the different enantiomers of the Carvone compound? Carvone (a molecule with one stereocenter) forms two mirror-image forms or enantiomers. One form has a sweetish, minty smell, like spearmint leaves. Its mirror image has a spicy aroma with notes of rye, like caraway seeds. Spearmint leaves and caraway seeds are two of the largest natural sources for the extraction of the two isomeric forms of carvone. What does the ability of humans to smell different enantiomers tell about human bodies? The fact that the two enantiomers are perceived as smelling differently is evidence that olfactory receptors in the human nose contain chiral groups, allowing them to respond more strongly to one enantiomer than to the other. Many, but not all enantiomers have unique and distinguishable odors. How do different enantiomers behave compared to each other with melting points, boiling points, density, and refractive index, etc? These physical properties would be the same between the enantiomers. While the behavior of enantiomers in biological systems can be quite different, an interesting note is that the physical properties of pairs of enantiomers are identical. Why can mixtures of enantiomers of a given compound be very challenging to separate from one another? Because the physical properties of pairs of enantiomers are identical (can't boil them to separate etc.) What device is used to determine the percent composition of an unknown mixture of enantiomers? A polarimeter How does a polarimeter work? A polarimeter uses a beam of plane-polarized light to interact with a sample of a chiral compound of unknown enantiomeric composition. The chiral molecules cause the plane of the polarization of the beam of light to rotate. Based on the direction and magnitude of rotation, the % composition (what % R and % S) of the sample can be determined. The rotation of light by individual enantiomers is always equal but opposite. Under carefully controlled and standardized conditions, the measurement of the optical activity of a pure single enantiomer of a compound gives a value known as the specific rotation. What is specific rotation? Specific rotation is the amount a compound rotates light per concentration of the molecule and length of the tube through which the light passes. It is the measurement of the optical activity of a pure single enantiomer of a compound. The specific rotation is a unique property of each enantiomer that can be used to help identify a compound, just as with physical constants like melting and boiling points What is the R/S system or the Cahn-Ingold-Prelog(CIP) system? What specifically does it tell us? The nomenclature system used to name enantiomeric forms of a chiral molecule. This system determines the direction of the "twist" of the groups attached to a stereocenter and incorporates a description of that direction into the name of the compound. What are the R/S designations? One enantiomer will be known as the "R" enantiomer (from the Latin "rectus"), while the mirror image will be known as the "S" enantiomer (from the Latin "sinister"). The R/S designation describes the configuration of the groups around a given stereocenter. What happens to the number of stereoisomers when a molecule has more than one stereocenter? Molecules that possess more than one stereocenter become more complex since increasing the number of stereocenters is associated with increasing numbers of stereoisomeric forms in which the compound can exist. With molecules that possess multiple stereocenters, an important skill is to be able to determine how many stereoisomers will exist for that compound and what the relationships are (how the individual stereoisomers are related to each other). Each stereocenter has a pair of enantiomers. So if a compound has two stereocenters there will be 4 stereoisomers possible. What formula is used to quickly determine the maximum number of individual stereoisomers possible for a chiral compound? 2^n (where n is the number of stereocenters in a compound) The rule says "maximum number", as some structural feature of certain molecules will result in not all of the predicted number of individual stereoisomers existing. 2-bromo-3-chlorobutane stereoisomers This molecule contains two stereocenters. Each stereocenter can exist in either an R or S configuration. Since there are two stereocenters, the permutations are, R, R; S, S; R, S; or S, R,. The structural formulae can be drawn to represent the four structures using wedge-and dash notation. Typically, when representing molecules with more than one stereocenter, the structures are presented with the longest carbon chain written vertically and each stereocenter presented in an eclipsed conformation (using wedge and dash notation) to make the comparisons between the individual stereoisomers more convenient Stereoisomers one and two form a pair of enantiomers. Stereoisomers three and four also form a pair of enantiomers. Thus far, it has been determined that 2-bromo-3-chlorobutane exists as two pairs of enantiomers (four total stereoisomers). What formula is used to find the number of enantiomer pairs for a compound that has multiple stereocenters? (2^n)/2 Where n is the number of stereocenters Cross-pairings of stereoisomers Relationships between the stereoisomers outside of their enantiomer pairs. Example: What is the relationship between stereoisomers one and three? What about one and four? How would we describe any cross-pairing, 1/3,1/4, 2/3,2/4? Diastereomers stereoisomers that are not mirror images of one another (they are cross-pairs, not enantiomers. This can be stated as the relationship between stereoisomers 1 and 3, 2 and 3, 1 and 4, and 2 and 4 is diastereomeric, or that these compounds represent pairs of diastereomers. Compare this to compounds 1 and 2, as well as 3 and 4, which represent pairs of enantiomers (or that their relationship is enantiomeric). Which word would describe the relationship between cis/trans pairs of molecules? They are diastereomers If either the cis or the trans stereoisomer was held up to a mirror, the mirror image would be the same (the mirror image of cis is not trans, and the mirror image of trans is not cis). Thus, since they are stereoisomers that are not mirror images of one another, cis-trans pairs are diastereomers. How do physical and chemical properties of diastereomer pairs differ from properties of enantiomer pairs? While pairs of enantiomers will have the same physical and chemical properties as one another, diastereomers (because they are not mirror images) will not. Diastereomers may have vastly different physical and chemical properties from one another. They may have drastically different melting and boiling points, solubilities, etc. In short, diastereomers behave as two different chemical substances. In practical applications, the separation of mixtures of diastereomers is much easier using common laboratory methods, which take advantage of differences in chemical and physical properties between compounds. In general why does the 2^n rule for predicting maximum stereoisomers not always work? The rule says "maximum number" as there are some structural features of certain molecules that result in not all of the predicted number of individual stereoisomers existing in reality. Why does the 2^n formula not correctly predict the number of stereoisomers for 2,3 dichlorobutane? This molecule has two stereocenters (carbons 2 and 3). Using the rule to predict the maximum number of individual stereoisomers, a maximum possibility of four (2^n = 2^2 = 4) would be determined. After drawing out the 4 stereoisomers we can see that stereoisomers one and two represent a pair of enantiomers, but stereoisomers three and four are different. Although three and four are indeed mirror images of one another, if one is rotated by 180° in the plane of the paper, it becomes superimposable on the other (all the atoms and groups line up exactly on both molecules), so they are the same compound. meso compound A molecule that contains stereocenters but is superimposable on its own mirror image. Due to this, meso compounds are achiral. The compound 2,3-dichlorobutane exists as three different stereoisomers: a pair of enantiomers and a meso compound. What makes a meso compound possible? An internal plane of symmetry. Meso compounds typically have an internal mirror plane of symmetry within their molecular structure. In this molecule, the presence of the two chlorine atoms allows for a plane of symmetry to be created when the chlorines are present on the same side of the carbon chain when written vertically. This internal plane of symmetry allows for this particular stereoisomer to be superimposable on its own mirror image (after a rotation of 180 degrees). Meso compounds would be diastereomers to the enantiomers, and would therefore have different physical and chemical properties. How do the physical and chemical properties of a meso compound compare to the properties of the enantiomers? Meso compounds would be diastereomers to the enantiomers, and would therefore have different physical and chemical properties. Fischer projection A method for representing the structures of chiral molecules in 2D - The carbon representing the stereocenter is usually omitted and is represented instead by the crossing point of horizontal and vertical lines. - The vertical and horizontal lines represent things bonded to the stereocenter. - Horizontal bonds are equivalent to "wedge bonds" (from wedge-and-dash notation). These bonds represent things that project towards the reader (out of the plane of the paper). - Vertical lines are equivalent to "dash bonds" and represent things that project away from the reader (behind the plane of the paper). What is the rule when using Fischer projections for moving a projections? The only "allowed" move is a rotation of 180 degrees in the plane of the paper. No "flips" or rotations other than 180 degrees. Unallowed moves will change the horizontal and vertical bonds and give an incorrect representation of the Fischer projection.