c6 primary, secondary, tertiary and, Schemes and Mind Maps of German

Download c6 primary, secondary, tertiary and and more Schemes and Mind Maps German in PDF only on Docsity! Section C – Functional groups C6 PRIMARY, SECONDARY, TERTIARY AND QUATERNARY NOMENCLATURE Definition The primary (1), secondary (2), tertiary (3) and quaternary (4) nomenclature is used in a variety of situations: to define a carbon center, or to define functional groups such as alcohols, halides, amines and amides. Identifying functional groups in this way can be important since the properties and reactivities of these groups may vary depending on whether they are primary, secondary, tertiary, or quaternary. Carbon centers One of the easiest ways of determining whether a carbon center is 1, 2, 3 or 4 is to count the number of bonds leading from that carbon center to another carbon atom (Fig. 1). A methyl group (CH3) is a primary carbon center, a methylene group (CH2) is a secondary carbon center, a methine group (CH) is a tertiary carbon center, and a carbon center with four alkyl substituents (C) is a quaternary carbon center (Fig. 2). Key Notes Carbon centers, as well as some functional groups (alcohols, alkyl halides, amines and amides), can be defined as primary (1), secondary (2), tertiary (3) or quaternary (4). Carbon centers can be identified as primary, secondary, tertiary, or quater- nary depending on the number of bonds leading to other carbon atoms. A methyl group contains a primary carbon center. A methylene group (CH2) contains a secondary carbon center. The methine group (CH) contains a tertiary carbon center while a carbon atom having four substituents is a quaternary center. Amines and amides can be defined as being primary, secondary, tertiary, or quaternary depending on the number of bonds leading from nitrogen to carbon. Alcohols and alkyl halides are defined as primary, secondary, or tertiary depending on the carbon to which the alcohol or halide is attached. The assignment depends on the number of bonds from that carbon to other car- bon atoms. It is not possible to get quaternary alcohols or quaternary alkyl halides. Recognition of functional groups (C1) Alcohols and alkyl halides Amines and amides Definition Carbon centers Related topic Amines and Amines and amides can be defined as being primary, secondary, tertiary, or qua- amides ternary depending on the number of bonds from nitrogen to carbon (Fig. 3). Note that a quaternary amine is positively charged and is therefore called a quaternary ammonium ion. Note also that it is not possible to get a quaternary amide. Alcohols and Alcohols and alkyl halides can also be defined as being primary, secondary, or ter- alkyl halides tiary (Fig. 4). However, the definition depends on the carbon to which the alcohol or halide is attached and it ignores the bond to the functional group. Thus, qua- ternary alcohols or alkyl halides are not possible. The following examples (Fig. 5) illustrate different types of alcohols and alkyl halides. 44 Section C – Functional groups R C H H H C H H R R R C R H R C R R R R c) d)a) b) Fig. 1. Carbon centers; (a) primary; (b) secondary; (c) tertiary; (d) quaternary. H3C CH3 CH3 CH3 CH3 2o 1o 3o 1o 1o 1o 4o 2o 1o 2o 2o Fig. 2. Primary, secondary, tertiary, and quaternary carbon centers. R N R R R N R R RR N R H N H H R + a) 3o1o 4o 2o Fig. 3. (a) Amines; (b) amides. N H R C R C O N H H O R R C O N R R 3o2o b) 1o R C H H X C X H R R R C R R X c)b)a) Fig. 4. Alcohols and alkyl halides; (a) primary; (b) secondary; (c) tertiary. H3C H3C Br Br H3C CH3 Br H3C CH3 CH3 1o 2o 3o a) b) c) Fig. 5. (a) 1 alkyl bromide; (b) 2 alkyl bromide; (c) 3 alkyl bromide; (d) 1 alcohol; (e) 2 alcohol; (f) 3 alcohol. 1o 2o 3o CH3 OH CH3 H3CH3C OH CH3 OH CH3 H3C d) e) f) D2 – Configurational isomers – alkenes and cycloalkanes 47 Alkenes – cis Alkenes having identical substituents at either end of the double bond can only and trans exist as one molecule. However, alkenes having different substituents at both ends isomerism of the double bond can exist as two possible isomers. For example, 1-butene (Fig. 1a) has two hydrogens at one end of the double bond and there is only one way of constructing it. On the other hand, 2-butene has different substituents at both ends of the double bond (H and CH3) and can be constructed in two ways. The methyl groups can be on the same side of the double bond (the cis isomer; Fig. 1b), or on opposite sides (the trans isomer; Fig. 1c). The cis and trans isomers of an alkene are configurational isomers (also called geometric isomers) because they have different shapes and cannot interconvert since the double bond of an alkene cannot rotate. Therefore, the substituents are ‘fixed’ in space relative to each other. The structures are different compounds with different chemical and physical properties. Alkenes – Z and The cis and trans nomenclature for alkenes is an old method of classifying the E nomenclature configurational isomers of alkenes and is still commonly used. However, it is only suitable for simple 1,2-disubstituted alkenes where one can compare the relative position of the two substituents with respect to each other. When it comes to trisubstituted and tetrasubstituted alkenes, a different nomenclature is required. The Z/E nomenclature allows a clear, unambiguous definition of the configu- ration of alkenes. The method by which alkenes are classified as Z or E is illus- trated in Fig. 2. First of all, the atoms directly attached to the double bond are identified and given their atomic number (Fig. 2b). The next stage is to compare the two atoms at each end of the alkene. The one with the highest atomic number takes priority over the other (Fig. 2c). At the left hand side, oxygen has a higher atomic number than hydrogen and takes priority. At the right hand side, both atoms are the same (carbon) and we cannot choose between them. Therefore, we now need to identify the atom of highest atomic number attached to each of these identical carbons. These correspond to a hydrogen for the methyl substituent and a carbon for the ethyl substituent. These are now different and so a priority can be made (Fig. 3a). Having identified which groups have priority, we can now see whether the priority groups are on the same side of the double bond or on opposite sides. If the two priority groups are on the same side of the double bond, the alkene is designated as Z (from the German word ‘zusammen’ meaning together). If the two priority groups are on opposite sides of the double bond, the CH3 H H H H3C C C H H CH3 H C C H CH3 CH3 a) b) c) Fig. 1. (a) 1-Butene; (b) cis-2-butene; (c) trans-2-butene. C C CH3O H CH3 CH2CH3 C C O H C C C C O H C C c)a) b) 6 6 Priority No difference 1 8 6 8 6 1 Fig. 2. (a) Alkene; (b) atomic numbers; (c) priority groups. 48 Section D – Stereochemistry alkene is designated as E (from the German word ‘entgegen’ meaning across). In this example, the alkene is E (Fig. 3b). Cycloalkanes Substituted cycloalkanes can also exist as configurational isomers. For example, there are two configurational isomers of 1,2-dimethylcyclopropane depending on whether the methyl groups are on the same side of the ring or on opposite sides (Fig. 4). The relative positions of the methyl groups can be defined by the bonds. A solid wedge indicates that the methyl group is coming out the page towards you, whereas a hatched wedge indicates that the methyl group is pointing into the page away from you. If the substituents are on the same side of the ring, the structure is defined as cis. If they are on opposite sides, the structure is defined as trans. C C O H C C H C C C CH3O H CH3 CH2CH3 8 6 Priority 1 1 Priority b) Fig. 3. (a) Choosing priority groups; (b) (E)-1-methoxy-2-methyl-1-butene. H3C CH3 H H H3C H H CH3 a) b) Fig. 4. (a) cis-1,2-Dimethylcyclopropane; (b) trans-1,2-dimethylcyclopropane.