diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--2b33a-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--2b33a-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png
index 6aa77ba2e1..1b2411c358 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--3c572-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--3c572-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png
index 3d40c2670a..f5e32ceaa7 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--5a557-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--5a557-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png
index 6aa77ba2e1..1b2411c358 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--64708-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--64708-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png
index 3d40c2670a..f5e32ceaa7 100644
Binary files a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--64708-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png and b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--64708-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png differ
diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--ad04e-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--ad04e-f-connection-between-Phosphate-and-RNA-to-SVG-2-chromium-linux.png
index 6aa77ba2e1..1b2411c358 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--f0889-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Import-Saving-Files/saving-svg.spec.ts-snapshots/Saving-in-svg-files-Export-to-SVG-Verify-it--f0889-f-connection-between-Phosphate-and-RNA-to-SVG-1-chromium-linux.png
index 3d40c2670a..f5e32ceaa7 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Sequence-Mode/sequence-mode.spec.ts-snapshots/Sequence-Mode-Side-chain-connections-between-sugar-and-phosphate-2-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Sequence-Mode/sequence-mode.spec.ts-snapshots/Sequence-Mode-Side-chain-connections-between-sugar-and-phosphate-2-chromium-linux.png
index 6484c95ff8..b4b6453fe9 100644
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diff --git a/ketcher-autotests/tests/Macromolecule-editor/Sequence-Mode/sequence-mode.spec.ts-snapshots/Sequence-Mode-Validate-displaying-modified-nuc-b031d-types-of-connection-between-Phosphate-and-RNA-1-chromium-linux.png b/ketcher-autotests/tests/Macromolecule-editor/Sequence-Mode/sequence-mode.spec.ts-snapshots/Sequence-Mode-Validate-displaying-modified-nuc-b031d-types-of-connection-between-Phosphate-and-RNA-1-chromium-linux.png
index 3d40c2670a..f5e32ceaa7 100644
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diff --git a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
index 5cde5140a1..acf95fdd9b 100644
--- a/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
+++ b/packages/ketcher-core/src/domain/entities/monomer-chains/Chain.ts
@@ -51,24 +51,36 @@ export class Chain {
   public add(monomer: BaseMonomer) {
     this.createSubChainIfNeed(monomer);
 
-    const nextMonomer = getNextMonomerInChain(monomer);
-
-    if (monomer instanceof Sugar && isValidNucleoside(monomer)) {
-      this.lastSubChain.add(Nucleoside.fromSugar(monomer));
-    } else if (monomer instanceof Sugar && isValidNucleotide(monomer)) {
-      this.lastSubChain.add(Nucleotide.fromSugar(monomer));
-    } else if (monomer instanceof Peptide) {
+    if (monomer instanceof Sugar) {
+      if (isValidNucleoside(monomer)) {
+        this.lastSubChain.add(Nucleoside.fromSugar(monomer));
+        return;
+      }
+      if (isValidNucleotide(monomer)) {
+        this.lastSubChain.add(Nucleotide.fromSugar(monomer));
+        return;
+      }
+    }
+    if (monomer instanceof Peptide) {
       this.lastSubChain.add(new MonomerSequenceNode(monomer));
-    } else if (
+      return;
+    }
+    const nextMonomer = getNextMonomerInChain(monomer);
+    const isNextMonomerNucleosideOrNucleotideOrPeptide = () => {
+      const isNucleosideOrNucleotide =
+        nextMonomer instanceof Sugar &&
+        (isValidNucleotide(nextMonomer) || isValidNucleoside(nextMonomer));
+      return isNucleosideOrNucleotide || nextMonomer instanceof Peptide;
+    };
+    if (
       monomer instanceof Phosphate &&
-      (this.lastNode instanceof Nucleoside ||
-        (nextMonomer instanceof Sugar &&
-          (isValidNucleotide(nextMonomer) || isValidNucleotide(nextMonomer))))
+      (!this.lastNode || this.lastNode instanceof Nucleoside) &&
+      (!nextMonomer || isNextMonomerNucleosideOrNucleotideOrPeptide())
     ) {
       this.lastSubChain.add(new MonomerSequenceNode(monomer));
-    } else {
-      this.lastSubChain.add(new LinkerSequenceNode(monomer));
+      return;
     }
+    this.lastSubChain.add(new LinkerSequenceNode(monomer));
   }
 
   public addNode(node: SubChainNode) {
@@ -105,7 +117,12 @@ export class Chain {
     return nodes;
   }
 
-  public get lastNode() {
+  public get lastNode():
+    | EmptySequenceNode
+    | MonomerSequenceNode
+    | Nucleoside
+    | Nucleotide
+    | undefined {
     return this.lastSubChain?.lastNode;
   }
 
diff --git a/packages/ketcher-core/src/domain/helpers/monomers.ts b/packages/ketcher-core/src/domain/helpers/monomers.ts
index 9400fc0315..f3db941b49 100644
--- a/packages/ketcher-core/src/domain/helpers/monomers.ts
+++ b/packages/ketcher-core/src/domain/helpers/monomers.ts
@@ -86,22 +86,30 @@ export function isMonomerBeginningOfChain(
   );
 }
 
-export function isValidNucleotide(sugar: Sugar) {
+export function isValidNucleotide(sugar: Sugar): boolean {
+  if (!getRnaBaseFromSugar(sugar)) {
+    return false;
+  }
+
   const phosphate = getPhosphateFromSugar(sugar);
-  const nextMonomerAfterPhosphate = getNextMonomerInChain(phosphate);
+  if (!phosphate) {
+    return false;
+  }
 
-  return Boolean(
-    getRnaBaseFromSugar(sugar) &&
-      getPhosphateFromSugar(sugar) &&
-      nextMonomerAfterPhosphate,
-  );
+  const nextMonomerAfterPhosphate = getNextMonomerInChain(phosphate);
+  return !!nextMonomerAfterPhosphate;
 }
 
-export function isValidNucleoside(sugar: Sugar) {
+export function isValidNucleoside(sugar: Sugar): boolean {
+  if (!getRnaBaseFromSugar(sugar)) {
+    return false;
+  }
+
   const phosphate = getPhosphateFromSugar(sugar);
-  const nextMonomerAfterPhosphate = getNextMonomerInChain(phosphate);
+  if (!phosphate) {
+    return true;
+  }
 
-  return (
-    getRnaBaseFromSugar(sugar) && (!phosphate || !nextMonomerAfterPhosphate)
-  );
+  const nextMonomerAfterPhosphate = getNextMonomerInChain(phosphate);
+  return !nextMonomerAfterPhosphate;
 }